In this paper, an in-host HIV infection model with latent reservoir, delayed CTL immune response and immune impairment is investigated. By using suitable Lyapunov functions and LaSalle's invariance principle, it is shown that when time delay is equal to zero, the immunity-inactivated reproduction ratio is a threshold determining the global dynamics of the model. By means of the persistence theory for infinite dimensional systems, it is proven that if the immunity-inactivated reproduction ratio is greater than unity, the model is permanent. Choosing time delay as the bifurcation parameter and analyzing the corresponding characteristic equation of the linearized system, the existence of a Hopf bifurcation at the immunity-activated equilibrium is established. Numerical simulations are carried out to illustrate the theoretical results and reveal the effects of some key parameters on viral dynamics.
Citation: Ning Bai, Rui Xu. Mathematical analysis of an HIV model with latent reservoir, delayed CTL immune response and immune impairment[J]. Mathematical Biosciences and Engineering, 2021, 18(2): 1689-1707. doi: 10.3934/mbe.2021087
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Abstract
In this paper, an in-host HIV infection model with latent reservoir, delayed CTL immune response and immune impairment is investigated. By using suitable Lyapunov functions and LaSalle's invariance principle, it is shown that when time delay is equal to zero, the immunity-inactivated reproduction ratio is a threshold determining the global dynamics of the model. By means of the persistence theory for infinite dimensional systems, it is proven that if the immunity-inactivated reproduction ratio is greater than unity, the model is permanent. Choosing time delay as the bifurcation parameter and analyzing the corresponding characteristic equation of the linearized system, the existence of a Hopf bifurcation at the immunity-activated equilibrium is established. Numerical simulations are carried out to illustrate the theoretical results and reveal the effects of some key parameters on viral dynamics.
1.
Introduction
Combination antiretroviral therapy or highly active antiretroviral therapy (HAART) have led to a substantial reduction in the incidence of HIV-related morbidity and mortality [1,2]. HAART consisting of at least three different drugs has proved to be effective in suppressing the plasma viral load of most patients to below 50 RNA copies/ml, which is the detection limit of current standard assays [3]. However, this does not mean that virus replication has been completely suppressed by the therapy [4,5,6]. Even in patients whose plasma viral level has been below the detection limit for many years, a low level of viremia can be detected in plasma by more sensitive assays [7]. Studies have shown that this phenomenon may be related to the continuous release of virus particles, which are produced by activating latently infected cells [8]. In the past decades, the activation of latently infected cells has been incorporated into the modelling of HIV infection [9,10,11,12,13].
Rong et al. [13] considered a mathematical model including uninfected CD4+ T cells T, latently infected CD4+ T cells L, actively infected CD4+ T cells T∗ and free virus V to explore a hypothesis about latently infected cell activation under the effect of therapy. The model takes the following form:
In (1.1), λ is the production rate of uninfected cells, dT is the death rate coefficient of uninfected cells, k is the infection rate coefficient at which uninfected cells are infected by free virus, and ε(0≤ε≤1) is an overall therapy efficacy. αL is the proportion of cells progress from uninfected to latently infected, a is the rate coefficient at which latently infected cells translate to actively infected cells, and dL is the death rate coefficient of latently infected cells. δ is the death rate coefficient of actively infected cells, N is the number of virus particles produced by an actively infected cell during its life time, and c is the rate coefficient at which free virus is cleared.
Noting that in system (1.1), the cytotoxic T-lymphocyte (CTL) immune response is ignored. Faced with viral infection, the immune system has a strong CTL immune response, which attacks actively infected cells to reduce viral load and protect infected individuals from virus-related diseases [14,15]. In addition, it is noteworthy that the generation of CTL cells at time t may depend on the number of actively infected cells at time t−τ, where the nonnegative constant τ represents a time delay of CTL immune response. Accordingly, a large number of HIV infection models with CTL immune response given by delay differential equations have been studied by several scholars, mainly focusing on the effect of time delay on the dynamics of the model, bifurcations, and several complex dynamical behaviors (see, for example, [16,17,18]). In [17], Wang et al. proposed a viral model with delayed immune response, where the specific expression of CTL cells is as follows:
˙z(t)=cy(t−τ)−bz(t),
in which y and z represent the numbers of actively infected cells and CTL cells, respectively. The parameters c and b are the coefficients of proliferation rate and dacay rate of CTL cells, respectively.
Furthermore, in most viral infection models, it is assumed that the presence of antigen can only simulate the immune response, and ignore the immune impairment. In fact, several human pathogens have the ability to suppress immune responses, allowing them to establish a persistent and productive infection that eventually lead to diseases [19,20,21]. Under this assumption, many researchers have carried out further researches on HIV infection [22,23,24], which helps us to understand the biological interactions between virus and immune system. In [24], Wang et al. considered a delayed viral model with immune impairment, where the specific expression of CTL cells is as follows:
˙z(t)=cy(t−τ)−bz(t)−myz.
Motivated by the works of Rong et al. [13] and Wang et al. [24], in the present paper, we are concerned with the joint effects of latent reservoir, delayed CTL immune response and immune impairment on the transmission dynamics of HIV infection. To this end, we consider the following delay differential equations:
In [25], Wodarz et al. found that the decay rate of free virus is much faster than that of infected cells. This allows us to make a quasi steady-state assumption: dv/dt=0, which implies v=Nay/σ, in other words, the number of free virus is proportional to the number of actively infected cells. Therefore, the number of actively infected cells y(t) can also be considered as a measure of free virus v(t), then system (1.2) can be described as the following system:
For system (1.3), the suitable phase space is R×R×C×R, where C=C([−τ,0],R) is the Banach space of all continuous functions mapping the interval [−τ,0] into R, with norm ‖ϕ‖=sup−τ≤θ≤0|ϕ(θ)| for ϕ∈C. The nonnegative cone of C is C+=C([−τ,0],R+). The initial condition for system (1.3) takes the form
It is well-known by the fundamental theory of functional differential equations [26], system (1.3) has a unique solution (x(t),u(t),y(t),z(t)) satisfying initial condition (1.4).
The organization of this paper is as follows. In section 2, we show the positivity and boundedness of solutions of system (1.3), and establish the existence of feasible equilibria of system (1.3). In section 3, we investigate the global asymptotic stability of each of feasible equilibria. In section 4, we verify that system (1.3) is permanent if the immunity-activated equilibrium exists. In section 5, we establish the existence of Hopf bifucation at the immune-activated equilibrium. In section 6, we present numerical simulation to illustrate the theoretical results, and explore the effects of some key parameters on viral dynamics by sensitivity analysis. The paper ends with a brief conclusion in section 7.
2.
Preliminaries
In this section, we demonstrate that system (1.3) with initial condition (1.4) is well-posed, and establish the existence of feasible equilibria.
2.1. Positivity and boundedness of solutions
Theorem 2.1.All solutions of system (1.3) with initial condition (1.4) are defined on [0,+∞) and remain positive for all t≥0 in R×R×C×R.
Proof. Firstly, we prove that x(t) is positive for all t≥0. Assume the contrary and let t1>0 be the first time such that x(t1)=0. Then from the first equation of system (1.3), we have ˙x(t1)=λ>0, which indicates that x(t)<0 for t∈(t1−ε1,t1), where ε1 is an arbitrarily small positive constant. This contradicts with the fact of x(t)>0 for all t∈[0,t1). It follows that x(t)>0 for all t≥0.
Similarly, we show that u(t), y(t) and z(t) are positive for all t≥0. Assume the contrary and let t2>0 be the first time such that y(t2)=0. Then from the third equation of system (1.3), we have ˙y(t2)=δu(t2). Solving u(t) in the second equation of system (1.3), we obtain
u(t2)=(φ2(0)+qβ∫t20x(s)y(s)e(μ+δ)sds)e−(μ+δ)t2>0,
which yields ˙y(t2)>0. It follows that y(t)>0 for all t≥0. Accordingly, from the second and fourth equations of system (1.3), we get
lim supt→+∞B(t)≤λmin{d,μ,a}=Production rate of uninfected CD4+ T cells×max{Lifespan of uninfected, latently infected or actively infected CD4+ T cells}.
Hence, for ε>0 sufficiently small, there is a T1>0 such that if t>T1,
x(t)+u(t)+y(t)=B(t)≤λmin{d,μ,a}+ε.
Furthermore, we derive from the fourth equation of system (1.3), for t>T1+τ,
Since this inequality holds true for arbitrary ε>0 sufficiently small, we conclude that
lim supt→+∞z(t)≤cλbmin{d,μ,a}.
Therefore, x(t), u(t), y(t) and z(t) are uniformly ultimately bounded. This completes the proof.
2.2. Reproduction ratio and feasible equilibria
System (1.3) is an autonomous differential equation system with a fixed time delay. It always admits a unique infection-free equilibrium E0=(x0,0,0,0), where x0=λ/d. In the following, applying the method in Diekmann et al. [27] and van den Driessche et al. [28], we compute the immunity-inactivated reproduction ratio R0 of system (1.3).
The infected compartments in system (1.3) are u and y, ordered (u,y). The nonlinear terms with new infection F and the outflow term V are given by
F=(qβxy(1−q)βxy),V=((μ+δ)u−δu+ay+pyz).
Evaluating the derivatives of F and V at the equilibrium E0 leads to the following matrices
F=(0qβλd0(1−q)βλd),V=(μ+δ0−δa).
Therefore, we obtain the following next-generation matrix
FV−1=(qβλδad(μ+δ)qβλad(1−q)βλδad(μ+δ)(1−q)βλad).
One of the eigenvalues of matrix FV−1 is 0, the other one gives the immunity-inactivated reproduction ratio of system (1.3)
R0=ρ(FV−1)=(1−q)βλad+qβλδad(μ+δ),
where ρ(FV−1) denotes the spectral radius of matrix FV−1. Besides, R0 represents the number of newly actively infected CD4+ T cells generated from one actively infected CD4+ T cell in a totally susceptible cells during its lifespan.
It is easy to see that if R0>1, in addition to the equilibrium E0, system (1.3) has an immunity-activated equilibrium E∗=(x∗,u∗,y∗,z∗), where
x∗=λd+βy∗,u∗=qβλy∗(μ+δ)(d+βy∗),z∗=cy∗b+my∗,
and y∗ is a unique positive real root of the following algebraic equation:
In this section, by using suitable Lyapunov functionals and LaSalle's invariance principle, we are concerned with the global asymptotic stability of each of feasible equilibria to system (1.3).
Theorem 3.1.If R0≤1, then the infection-free equilibrium E0=(x0,0,0,0) of system (1.3) is globally asymptotically stable for any time delay τ≥0.
Proof. Let (x(t),u(t),y(t),z(t)) be any positive solution of system (1.3) with initial condition (1.4). Define
It follows from (3.2) that W′1(t)≤0. By Theorem 5.3.1 in reference [29], solutions limit to M1, the largest invariant subset of {(x(t),u(t),y(t),z(t)):W′1(t)=0}. Clearly, we see from (3.2) that W′1(t)=0 if and only if x=x0 and z=0. Noting that M1 is invariant, for each element in M1, we have x(t)=x0 and z(t)=0. It follows from the first equation of system (1.3) that 0=x′(t)=−βx0y(t), which yields y(t)=0. Furthermore, it follows from the third equation of system (1.3) that 0=y′(t)=δu(t), which leads to u(t)=0. Hence, W′1(t)=0 if and only if x(t)=x0, u(t)=0, y(t)=0 and z(t)=0. Accordingly, E0 is globally asymptotically stable follows from LaSalle's invariance principle. This completes the proof.
Theorem 3.2.If R0>1, then the equilibrium E0 is unstable and the immunity-activated equilibrium E∗=(x∗,u∗,y∗,z∗) of system (1.3) is globally asymptotically stable when τ=0.
Proof. The characteristic equation of system (1.3) at the equilibrium E0 is
(s+d)(s+b)[s2+(μ+δ+a+(q−1)βλd)s+a(μ+δ)(1−R0)]=0.
(3.3)
It is clear that (3.3) always has two negative real roots λ1=−d, λ2=−b, and other roots are determined by the following equation:
f(s)=s2+(μ+δ+a+(q−1)βλd)s+a(μ+δ)(1−R0)=0.
(3.4)
If R0>1, it is easy to see that
f(0)=a(μ+δ)(1−R0)<0 andlims→+∞f(s)=+∞.
Noting that f(s) is a continuous function in respect to s, so (3.4) has at least one positive real root. Accordingly, (3.3) has at least one positive real root, and E0 is unstable.
Let (x(t),u(t),y(t),z(t)) be any positive solution of system (1.3) with initial condition (1.4). Define
It follows from (3.8) that W′2(t)≤0. By Theorem 5.3.1 in reference [29], solutions limit to M2, the largest invariant subset of {(x(t),u(t),y(t),z(t)):W′2(t)=0}. Clearly, we see from (3.8) that W′2(t)=0 if and only if x=x∗, u=u∗, y=y∗ and z=z∗. Accordingly, the global asymptotic stability of E∗ follows from LaSalle's invariance principle. This completes the proof.
4.
Permanence
In this section, we explore the permanence of system (1.3) referring to the persistence theory on infinite dimensional systems developed by Hale and Waltman [30].
Let X be a complete metric space with metric d. Assume that T is a continuous mapping from [0,+∞)×X into X with the following properties:
Tt∘Ts=Tt+s,T0(x)=x,t,s≥0,x∈X,
where Tt(x)=T(t,x). The distance d(x,Y) from a point x∈X to a subset Y of X is defined by
d(x,Y)=infy∈Yd(x,y).
Recall that the positive orbit γ+(x) through x is defined as γ+(x)=∪t≥0T(t)x, and its ω-limit set is ω(x)=∩s≥0¯∪t≥s{T(t)x}. Define Ws(A) the strong stable set of a compact invariant set A as
Ws(A)={x:x∈X,ω(x)≠∅,ω(x)⊂A}.
Suppose that X0 is an open set in X, X0⊂X, X0∩X0=∅ and X0∪X0=X. Moreover, T(t) is a C0−semigroup of X satisfying
T(t):X0⟶X0,T(t):X0⟶X0.
(4.1)
Let T∂(t)=T(t)|X0, and A∂ be the global attractor for T∂(t). The following result is provided.
Lemma 4.1.Suppose that T(t) satisfies (4.1) and the following conditions (Hale & Waltman [30]):
(i) There is a t0≥0 such that T(t) is compact for t>t0.
(ii) T(t) is point dissipative in X.
(iii) ~A∂=⋃x∈A∂ω(x) is isolated and has an acyclic covering ˜M, where ˜M={M1,M2,⋯,Mn}.
(iv) Ws(Mi)∩X0=∅, i=1,2,⋯,n.
Then X0 is a uniform repeller with respect to X0, that is, there is an ε0>0 such that for any x∈X0, lim inft→+∞d(T(t)x,X0)≥ε0, where d is the distance of T(t)x from X0.
We are now in a position to state and prove our result on the permanence of system (1.3) with initial condition (1.4).
Theorem 4.1.If R0>1, then system (1.3) is permanent.
It is easy to see that X0∩X0=∅ and X0∪X0=X. For any (ϕ1,ϕ2,ϕ3,ϕ4) in X, define T(t) for t≥0 as T(t)(ϕ1,ϕ2,ϕ3,ϕ4)=(x(t),u(t),y(t),z(t)), where (x(t),u(t),y(t),z(t)) is a solution of system (1.3) with initial condition (ϕ1,ϕ2,ϕ3,ϕ4). Then {T(t)}t≥0 is a C0−semigroup generated by system (1.3). By the definition of X0 and X0, we verify that X, X0 and X0 are all positively invariant.
According to Theorem 2.2, we obtain that condition (ii) of Lemma 4.1 is satisfied. Noting that the functions in right side of system (1.3) are in C1 and the solution of system (1.3) with initial condition (1.4) is ultimately bounded, using the smoothing property of solutions of delay differential equations introduced in Kuang (Theorem 2.8) [31], it follows that condition (i) of Lemma 4.1 is satisfied.
Note that system (1.3) admits one boundary equilibrium E0=(λ/d,0,0,0) in X0. For any solution of system (1.3) with initial condition (ϕ1(θ),ϕ2(θ),ϕ3(θ),ϕ4(θ))∈X0, we have u(t)=0, y(t)=0, z(t)=0 and x(t)→λ/d as t→∞. Hence {E0} contains all ω−limit sets in X0. By Theorem 3.2, E0 is unstable if R0>1. Accordingly, {E0} is isolated and has an acyclic covering satisfying the condition (iii) in Lemma 4.1.
We now show that Ws(E0)∩X0=∅. Assume Ws(E0)∩X0≠∅. Then there is a positive solution (x(t),u(t),y(t),z(t)) with limt→+∞(x(t),u(t),y(t),z(t))=(λ/d,0,0,0). Since R0>1, we can choose ε1>0 sufficiently small satisfying
λd−ε1>a(μ+δ)β[(1−q)μ+δ]+p(μ+δ)ε1β[(1−q)μ+δ].
(4.2)
For ε1>0 sufficiently small satisfying (4.2), there is a t0>0 such that if t>t0, we have
x(t)>λd−ε1 andz(t)≤ε1.
Hence, it follows from system (1.3) that, for t>t0,
It is easy to see that G2<0 when R0>1. Accordingly, g(s)=0 has at least one positive root λ∗. In this case, u1→∞ and y1→∞ as t→∞. By comparison arguments, it is shown that u→∞ and y→∞ as t→∞. This contradicts limt→+∞(x(t),u(t),y(t),z(t))=(λ/d,0,0,0). Hence, we have Ws(E0)∩X0=∅ satisfying the condition (iv) in Lemma 4.1. This completes the proof.
5.
Hopf bifurcation
In this section, we are concerned with the effect of time delay τ on the stability of the immunity-activated equilibrium E∗=(x∗,u∗,y∗,z∗).
The characteristic equation of system (1.3) at the equilibrium E∗ is
where ν=(−1+√3i)/2 and ξ is one of cubic roots of the complex number −Q/2+√D0. By [32], we have the following results.
Lemma 5.1.For polynomial equation (5.4), the following conclusions are valid (Yan & Li [32]):
(i) If C0<0, then (5.4) at least has one positive root.
(ii) Assume that C0≥0, then (5.4) has no positive roots if one of the following conditions holds:
(1) D0>0 and z∗1<0;
(2) D0=0 and z∗2<0;
(3) D0<0 and z∗3<0.
(iii) Assume that C0≥0, then (5.4) at least has one positive root if one of the following conditions holds:
(1) D0>0, z∗1>0 and h(z∗1)<0;
(2) D0=0, z∗2>0 and h(z∗2)<0;
(3) D0<0, z∗3>0 and h(z∗3)<0.
Without loss of generality, we assume that (5.4) has four positive real roots, which are denoted as z1, z2, z3 and z4, respectively. Then (5.3) has positive roots ωk=√zk(k=1,2,3,4). From (5.2) we have
where k=1,2,3,4 and n=1,2,⋯. Therefore, (5.1) has a pair of purely imaginary roots of the form ±ωki with τ=τ(n)k. Let s(τ)=ψ(τ)+iω(τ) be a root of (5.1) satisfying ψ(τ(n)k)=0, ω(τ(n)k)=ωk. Denote
τ0=mink∈{1,2,3,4}{τ(0)k},ω0=ωk0.
(5.5)
Differentiating (5.1) with respect τ, it follows that
From what has been discussed above, we have the following result.
Theorem 5.1.Let ω0 and τ0 be defined by (5.5). Assumed that R0>1, we have
(i) the equilibrium E∗ is locally asymptotically stable for all τ≥0 if the condition as stated in Lemma 4.1(ii) is satisfied.
(ii) the equilibrium E∗ is locally asymptotically stable for τ∈[0,τ0) if the condition as stated in Lemma 4.1(i) or Lemma 4.1(iii) is satisfied.
(iii) system (1.3) undergoes a Hopf bifurcation at the equilibrium E∗ when τ=τ0 if the condition as stated in (ii) is satisfied and h′(ω20)>0.
6.
Numerical simulation
In this section, numerical simulations will be given to illustrate the theoretical results in Theorem 5.1, and sensitivity analysis is used to determine key parameters affecting HIV infection. In addition, parameter values of system (1.3) are listed in Table 2.
Table 2.
Parameter values of system (1.3) used in numerical simulations.
We choose parameter values as listed in Table 2. By calculation, we get R0=16.8744>1, ω0=0.4838, τ0=3.7708 and h′(ω20)=0.0593>0. In this case, Theorem 5.1 ensures that the equilibrium E∗=(973.1423,2.4090,257.4517,4.3276) is locally asymptotically stable if τ<τ0, unstable if τ>τ0, and system (1.3) undergoes a Hopf bifurcation at E∗ when τ=τ0. Figure 1 shows the phase diagram of system (1.3) with initial conditions x(0)=873.1423, u(0)=1.4090, y(0)=207.4517 and z(0)=3.3276. It is worth mentioning that the solutions of all variables in system (1.3) are created by the command of dde23 in Matlab. Figure 1(a) shows that the solution of system (1.3) approaches E∗ as t goes to infinity when τ=3.5, and Figure 1(b) illustrates that E∗ losses its stability when τ=4. When τ varies from 3 to 5, the bifurcation diagram of system (1.3) is shown in Figure 2. From Figure 2, we obtain that the time delay τ can cause the equilibrium E∗ to be unstable when τ crosses τ0 to the right. It should be noted that the bifurcation diagram of system (1.3) is created by integrating the differential equation forward in time and plotting the maximum and minimum values of the periodic solutions using Matlab.
Figure 1.
The temporal solution found by numerical integration of system (1.3) with initial condition x(0)=873.1423, u(0)=1.4090, y(0)=207.4517, z(0)=3.3276, and parameter values are listed in Table 2, in which (a) τ=3.5<τ0 and (b) τ=4>τ0.
Figure 2.
The bifurcation diagram of system (1.3) with the initial condition x(0)=873.1423, u(0)=1.4090, y(0)=207.4517, z(0)=3.3276. Parameter τ varies from 3 to 5, and other parameters are listed in Table 2.
Studies have shown that the new generation of broadly neutralizing anti-HIV antibodies (bNAbs) can suppress new infection by blocking entry of virions, and current inducers can activate the latently infected cells both in vitro and in vivo[33]. More specifically, in our model, bNAbs mainly influence parameter β, and inducers affect parameter δ. Therefore, in this subsection, we analyze the effect of parameters β and δ on HIV infection.
From Theorems 3.1, 3.2 and 5.1, the immunity-inactivated reproduction ratio R0 is a threshold to determined whether actively infected cell dies out or prevails. Hence, we first explore the effects of parameters β and δ on R0 by Latin hypercube sampling with 1000 samples and Partial Rank Correlation Coefficient (see Figure 3). Figure 3 shows the Partial Rank Correlation Coefficients of R0 in respect to β and δ, which implies that β and δ are both positive correlative variables with R0, and β contributes more to R0 compared to δ.
Figure 3.
The tornado chart of PRCC for coefficients associated with R0.
Then, we perform the effects of β and δ on the number of actively infected cells by decreasing the same proportion of parameter values (see Figure 4). As shown from Figure 4, decreasing the values of β are more conducive to reduce the number of actively infected cells, while the values of δ has little effect, which is in agreement with Figure 3.
Figure 4.
The effects of the parameters β and δ on the number of actively infected cells with initial condition x(0)=873.1423, u(0)=1.4090, y(0)=207.4517, z(0)=3.3276, τ=2.5 and other parameters are listed in Table 2.
In this paper, we consider an HIV infection model with latent reservoir, delayed CTL immune response and immune impairment. Assuming that the number of actively infected cells y(t) can be considered as a measure of free virus v(t), then system (1.2) can be transformed into system (1.3). By a vigorous mathematical analysis, the threshold dynamics of system (1.3) is established and it can be determined by the immunity-inactivated reproduction ratio R0. If R0<1, the infection-free equilibrium E0 of system (1.3) is globally asymptotically stable for any CTL immune delay τ≥0. If R0>1, the immunity-activated equilibrium E∗ of system (1.3) is globally asymptotically stable when CTL immune delay τ=0. In addition, we see that a threshold τ0 for the CTL immune delay was identified to characterize the existence of Hopf bifurcation at the immunity-activated equilibrium E∗ when the CTL immune delay cross it. This implies that the introduction of the CTL immune delay τ plays an important role in destabilizing the the immunity-activated equilibrium and leading to periodic oscillation. Numerical simulations vividly illustrate our main results of stability analysis for system (1.3). In addition, we perform the sensitivity analysis of threshold parameters R0 and the number of actively infected cells y in respect to the parameters β and δ, which provides some suggestions for clinical treatment of HIV-associated diseases.
If the latent reservoir is not considered in our model, then system (1.3) becomes the model proposed in [24], the specific form is as follows:
where the descriptions of all variables and parameters in system (7.1) are consistent with system (1.3). By calculation, the immunity-inactivated reproduction ratio of system (7.1) is given as R0=λβ/(ad). Compared with the works in [24], it is found that incorporating the latent reservoir into an in-host HIV infection model could reduce the immunity-inactivated reproduction ratio, but the dynamics of the model does not change. If the latent reservoir and immune impairment are not considered in our model, then system (1.3) becomes the model proposed in [17]. Compared with the works in [17], it is found that the immune delay could cause stable switching even if the latent reservoir and immune impairment are not considered in the HIV infection model.
In addition, studies have found that uninfected cells can be infected through indirect virus-to-cell infection or direct cell-to-cell transmission [34,35]. Combining both virus-to-cell infection and cell-to-cell transmission into the model considered in this paper, we obtain the following system
It may be difficult to study the dynamics of system (7.2) without any assumptions, which is also what we need to break through in the future.
Acknowledgments
The authors wish to thank the Editor and reviewers for their valuable comments and suggestions that greatly improved the presentation of this work.
This work was supported by the National Natural Science Foundation of China (Grant Nos. 11871316 and 11801340), and the Natural Science Foundation of Shanxi Province (Grant Nos. 201801D121006 and 201801D221007).
Conflict of interest
All authors declare no conflicts of interest in this paper.
References
[1]
F. J. Palella, K. M. Delaney, A. C. Moorman, M. O. Loveless, J. Fuhrer, G. A. Satten, et al., Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection, N. Engl. J. Med., 338 (1998), 853–860. doi: 10.1056/NEJM199803263381301
[2]
E. L. Murphy, A. C. Collier, L. A. Kalish, S. F. Assmannet, M. F. Para, T. P. Flanigan, et al., Highly active antiretroviral therapy decreases mortality and morbidity in patients with advanced HIV disease, Ann. Int. Med., 135 (2001), 17–26. doi: 10.7326/0003-4819-135-1-200107030-00005
[3]
G. Dornadula, H. Zhang, B. VanUitert, J. Stern, L. Livornese Jr, M. J. Ingerman, et al., Residual HIV-1 RNA in blood plasma of patients taking suppressive highly active antiretroviral therapy, J. Am. Med. Assoc., 282 (1999), 1627–1632. doi: 10.1001/jama.282.17.1627
[4]
T. W. Chun, L. Stuyver, S. B. Mizell, L. A. Ehler, J. M. Mican, M. Baseler, et al., Presence of an inducible HIV-1 latent reservoir during highly active antiretroviral therapy, Proc. Nat. Acad. Sci., 94 (1997), 13193–13197. doi: 10.1073/pnas.94.24.13193
[5]
T. W. Chun, D. C. Nickle, J. S. Justement, D. Large, A. Semerjian, M. E. Curlin, et al., HIV-infected individuals receiving effective antiviral therapy for extended periods of time continually replenish their viral reservoir, J. Clin. Invest., 115 (2005), 3250–3255. doi: 10.1172/JCI26197
[6]
T. W. Chun, D. C. Nickle, J. S. Justement, J. H. Meyers, G. Roby, C. W. Hallahan, et al., Persistence of HIV in gut-associated lymphoid tissue despite long-term antiretroviral therapy, J. Infect. Dis., 197 (2008), 714–720. doi: 10.1086/527324
[7]
S. Palmer, A. P. Wiegand, F. Maldarelli, H. Bazmi, J. M. Mican, M. Polis, et al., New real-time reverse transcriptase-initiated PCR assay with single-copy sensitivity for human immunodeficiency virus type 1 RNA in plasma, J. Clin. Microbiol., 41 (2003), 4531–4536. doi: 10.1128/JCM.41.10.4531-4536.2003
[8]
T. W. Chun, D. Engel, S. B. Mizell, L. A. Ehler, A. S. Fauci, Induction of HIV-1 replication in latently infected CD4+ T cells using a combination of cytokines, J. Exp. Med., 188 (1998), 83–91. doi: 10.1084/jem.188.1.83
[9]
A. S. Perelson, P. Essunger, Y. Z. Cao, M. Vesanen, A. Hurley, K. Saksela, et al., Decay characteristics of HIV-1-infected compartments during combination therapy, Nature, 387 (1997), 188–191. doi: 10.1038/387188a0
[10]
V. Müller, J. F. Vigueras-Gómez, S. Bonhoeffer, Decelerating decay of latently infected cells during prolonged therapy for human immunodeficiency virus type 1 infection, J. Virol., 76 (2002), 8963–8965. doi: 10.1128/JVI.76.17.8963-8965.2002
[11]
H. Kim, A. S. Perelson, Viral and latent reservoir persistence in HIV-1-infected patients on therapy, PLoS Comput. Biol., 2 (2006), e135. doi: 10.1371/journal.pcbi.0020135
[12]
L. B. Rong, A. S. Perelson, Modeling latently infected cell activation: viral and latent reservoir persistence, and viral blips in HIV-infected patients on potent therapy, PLoS Comput. Biol., 5 (2009), e1000533. doi: 10.1371/journal.pcbi.1000533
[13]
L. B. Rong, A. S. Perelson, Asymmetric division of activated latently infected cells may explain the decay kinetics of the HIV-1 latent reservoir and intermittent viral blips, Math. Biosci., 217 (2009), 77–87. doi: 10.1016/j.mbs.2008.10.006
[14]
M. A. Nowak, C. R. M. Bangham, Population dynamics of immune responses to persistent viruses, Science, 272 (1996), 74–79. doi: 10.1126/science.272.5258.74
[15]
J. H. Cao, J. Mcnevin, S. Holte, L. Fink, L. Corey, M. J. McElrath, Comprehensive analysis of human immunodeficiency virus type 1 (HIV-1)-specific gamma interferon-secreting CD8+ T cells in primary HIV-1 infection, J. Virol., 77 (2003), 6867–6878. doi: 10.1128/JVI.77.12.6867-6878.2003
[16]
A. A. Canabarro, I. M. Gléria, M. L. Lyra, Periodic solutions and chaos in a non-linear model for the delayed cellular immune response, Physica A, 342 (2004), 234–241. doi: 10.1016/j.physa.2004.04.083
[17]
K. F. Wang, W. D. Wang, H. Y. Pang, X. Liu, Complex dynamic behavior in a viral model with delayed immune response, Physica D, 226 (2007), 197–208. doi: 10.1016/j.physd.2006.12.001
[18]
X. H. Tian, R. Xu, Global stability and Hopf bifurcation of an HIV-1 infection model with saturation incidence and delayed CTL immune response, Appl. Math. Comput., 237 (2014), 146–154.
[19]
N. L. Komarova, E. Barnes, P. Klenerman, D. Wodarz, Boosting immunity by antiviral drug therapy: a simple relationship among timing, efficacy, and success, Proc. Nat. Acad. Sci., 100 (2003), 1855–1860. doi: 10.1073/pnas.0337483100
[20]
A. Folgori, E. Spada, M. Pezzanera, L. Ruggeri, A. Mele, A. R. Garbuglia, et al., Early impairment of hepatitis C virus specific T cell proliferation during acute infection leads to failure of viral clearance, Gut, 55 (2006), 1012–1019. doi: 10.1136/gut.2005.080077
[21]
Y. Kuroda, H. Takashima, Impairment of cell-mediated immune responses in HTLV-I-associated myelopathy, J. Neurol. Sci., 100 (1990), 211–216. doi: 10.1016/0022-510X(90)90035-L
[22]
R. R. Regoes, D. Wodarz, M. A. Nowak, Virus dynamics: the effect of target cell limitation and immune responses on virus evolution, J. Theor. Biol., 191 (1998), 451–462. doi: 10.1006/jtbi.1997.0617
[23]
Z. P. Wang, X. N. Liu, A chronic viral infection model with immune impairment, J. Theor. Biol., 249 (2007), 532–542. doi: 10.1016/j.jtbi.2007.08.017
[24]
S. L. Wang, X. Y. Song, Z. H. Ge, Dynamics analysis of a delayed viral infection model with immune impairment, Appl. Math. Model., 35 (2011), 4877–4885. doi: 10.1016/j.apm.2011.03.043
[25]
D. Wodarz, J. P. Christensen, A. R. Thomsen, The importance of lytic and nonlytic immune responses in viral infections, Trends Immunol., 23 (2002), 194–200. doi: 10.1016/S1471-4906(02)02189-0
[26]
J. Hale, L. Verduyn, Introduction to Functional Differential Equations, Springer, New York, 1993.
[27]
O. Diekmann, J. A. P. Heesterbeek, J. A. J. Metz, On the definition and the computation of the basic reproduction ratio R0 in models for infectious diseases in heterogeneous populations, J. Math. Biol., 28 (1990), 365–382.
[28]
P. van den Driessche, J. Watmough, Reproduction numbers and sub-threshold endemic equilibria for compartmental models of disease transmission, Math. Biosci., 180 (2002), 29–48. doi: 10.1016/S0025-5564(02)00108-6
[29]
J. Hale, Theory of Functional Differential Equations, Springer, New York, 1976.
[30]
J. Hale, P. Waltman, Persistence in infinite-dimensional systems, SIAM J. Math. Anal., 20 (1989), 388–395. doi: 10.1137/0520025
[31]
Y. Kuang, Delay Differential Equations with Applications in Population Dynamics, Academic Press, New York, 1993.
[32]
X. Yan, W. Li, Stability and bifurcation in a simplified four-neuron BAM neural network with miltiple delays, Discrete Dyn. Nat. Soc., 2006 (2006), 1–29.
[33]
C. Yan, W. D. Wang, Modeling HIV Dynamics Under Combination Therapy with Inducers and Antibodies, Math. Biosci., 81 (2019), 2625–2648.
[34]
W. Hübner, G. P. McNerney, P. Chen, B. M. Dale, R. E. Gordon, F. Y. S. Chuang, et al., Quantitative 3D video microscopy of HIV transfer across T cell virological synapses, Science, 323 (2009), 1743–1747. doi: 10.1126/science.1167525
[35]
K. M. Law, N. L. Komarova, A. W. Yewdall, R. K. Lee, O. L. Herrera, et al., In vivo HIV-1 cell-to-cell transmission promotes multicopy micro-compartmentalized infection, Cell Rep., 15 (2016), 2771–2783. doi: 10.1016/j.celrep.2016.05.059
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Figure 1. The temporal solution found by numerical integration of system (1.3) with initial condition x(0)=873.1423, u(0)=1.4090, y(0)=207.4517, z(0)=3.3276, and parameter values are listed in Table 2, in which (a) τ=3.5<τ0 and (b) τ=4>τ0
Figure 2. The bifurcation diagram of system (1.3) with the initial condition x(0)=873.1423, u(0)=1.4090, y(0)=207.4517, z(0)=3.3276. Parameter τ varies from 3 to 5, and other parameters are listed in Table 2
Figure 3. The tornado chart of PRCC for coefficients associated with R0
Figure 4. The effects of the parameters β and δ on the number of actively infected cells with initial condition x(0)=873.1423, u(0)=1.4090, y(0)=207.4517, z(0)=3.3276, τ=2.5 and other parameters are listed in Table 2