Elevated Inflammation Associated with Markers of Neutrophil Function and Gastrointestinal Disruption in Pilot Study of Plasmodium fragile Co-Infection of ART-Treated SIVmac239+ Rhesus Macaques.

Human immunodeficiency virus (HIV) and malaria, caused by infection with Plasmodium spp., are endemic in similar geographical locations. As a result, there is high potential for HIV/Plasmodium co-infection, which increases the pathology of both diseases. However, the immunological mechanisms underlying the exacerbated disease pathology observed in co-infected individuals are poorly understood. Moreover, there is limited data available on the impact of Plasmodium co-infection on antiretroviral (ART)-treated HIV infection. Here, we used the rhesus macaque (RM) model to conduct a pilot study to establish a model of Plasmodium fragile co-infection during ART-treated simian immunodeficiency virus (SIV) infection, and to begin to characterize the immunopathogenic effect of co-infection in the context of ART. We observed that P. fragile co-infection resulted in parasitemia and anemia, as well as persistently detectable viral loads (VLs) and decreased absolute CD4+ T-cell counts despite daily ART treatment. Notably, P. fragile co-infection was associated with increased levels of inflammatory cytokines, including monocyte chemoattractant protein 1 (MCP-1). P. fragile co-infection was also associated with increased levels of neutrophil elastase, a plasma marker of neutrophil extracellular trap (NET) formation, but significant decreases in markers of neutrophil degranulation, potentially indicating a shift in the neutrophil functionality during co-infection. Finally, we characterized the levels of plasma markers of gastrointestinal (GI) barrier permeability and microbial translocation and observed significant correlations between indicators of GI dysfunction, clinical markers of SIV and Plasmodium infection, and neutrophil frequency and function. Taken together, these pilot data verify the utility of using the RM model to examine ART-treated SIV/P. fragile co-infection, and indicate that neutrophil-driven inflammation and GI dysfunction may underlie heightened SIV/P. fragile co-infection pathogenesis.

Effect of B-cell depletion on viral replication and clinical outcome of simian immunodeficiency virus infection in a natural host.

Simian immunodeficiency virus (SIV)-infected African nonhuman primates do not progress to AIDS in spite of high and persistent viral loads (VLs). Some authors consider the high viral replication observed in chronic natural SIV infections to be due to lower anti-SIV antibody titers than those in rhesus macaques, suggesting a role of antibodies in controlling viral replication. We therefore investigated the impact of antibody responses on the outcome of acute and chronic SIVagm replication in African green monkeys (AGMs). Nine AGMs were infected with SIVagm.sab. Four AGMs were infused with 50 mg/kg of body weight anti-CD20 (rituximab; a gift from Genentech) every 21 days, starting from day -7 postinfection up to 184 days. The remaining AGMs were used as controls and received SIVagm only. Rituximab-treated AGMs were successfully depleted of CD20 cells in peripheral blood, lymph nodes (LNs), and intestine, as shown by the dynamics of CD20+ and CD79a+ cells. There was no significant difference in VLs between CD20-depleted AGMs and control monkeys: peak VLs ranged from 10(7) to 10(8) copies/ml; set-point values were 10(4) to 10(5) SIV RNA copies/ml. Levels of acute mucosal CD4+ T-cell depletion were similar for treated and nontreated animals. SIVagm seroconversion was delayed for the CD20-depleted AGMs compared to results for the controls. There was a significant difference in both the timing and magnitude of neutralizing antibody responses for CD20-depleted AGMs compared to results for controls. CD20 depletion significantly altered the histological structure of the germinal centers in the LNs and Peyer's patches. Our results, although obtained with a limited number of animals, suggest that humoral immune responses play only a minor role in the control of SIV viral replication during acute and chronic SIV infection in natural hosts.

Simian immunodeficiency virus SIVrcm, a unique CCR2-tropic virus, selectively depletes memory CD4+ T cells in pigtailed macaques through expanded coreceptor usage in vivo.

Simian immunodeficiency virus SIVrcm, which naturally infects red-capped mangabeys (RCMs), is the only SIV that uses CCR2 as its main coreceptor due to the high frequency of a CCR5 deletion in RCMs. We investigated the dynamics of SIVrcm infection to identify specific pathogenic mechanisms associated with this major difference in SIV biology. Four pigtailed macaques (PTMs) were infected with SIVrcm, and infection was monitored for over 2 years. The dynamics of in vivo SIVrcm replication in PTMs was similar to that of other pathogenic and nonpathogenic lymphotropic SIVs. Plasma viral loads (VLs) peaked at 10(7) to 10(9) SIVrcm RNA copies/ml by day 10 postinoculation (p.i.). A viral set point was established by day 42 p.i. at 10(3) to 10(5) SIVrcm RNA copies/ml and lasted up to day 180 p.i., when plasma VLs decreased below the threshold of detection, with blips of viral replication during the follow-up. Intestinal SIVrcm replication paralleled that of plasma VLs. Up to 80% of the CD4(+) T cells were depleted by day 28 p.i. in the gut. The most significant depletion (>90%) involved memory CD4(+) T cells. Partial CD4(+) T-cell restoration was observed in the intestine at later time points. Effector memory CD4(+) T cells were the least restored. SIVrcm strains isolated from acutely infected PTMs used CCR2 coreceptor, as reported, but expansion of coreceptor usage to CCR4 was also observed. Selective depletion of effector memory CD4(+) T cells is in contrast with predicted in vitro tropism of SIVrcm for macrophages and is probably due to expansion of coreceptor usage. Taken together, these findings emphasize the importance of understanding the selective forces driving viral adaptation to a new host.

Limited ability of humoral immune responses in control of viremia during infection with SIVsmmD215 strain.

We investigated the impact of rhesus macaque (RM) B-cell depletion before inoculation with the isolate SIVsmmD215. Seven RMs were treated every 3 weeks with 50 mg/kg of an anti-CD20 antibody (rituximab) starting 7 days before inoculation for 2 (n = 4) and 5 (n = 3) months. Four control animals received no antibody. Three animals were completely depleted of CD20(+) B cells, but 4 were only partially depleted of CD20 cells in the LNs and intestine. The decrease in antibody production was consistent with the efficacy of tissue CD20 depletion. Seroconversion and neutralizing antibody production was significantly delayed in animals showing complete tissue CD20 depletion and remained at low titers in all CD20-depleted RMs. Surprisingly, there was no significant difference in acute or chronic viral loads between CD20-depleted and control animal groups. There was a tendency for lower viral set points in CD20-depleted animals. At 6 weeks after inoculation, cellular immune responses were significantly stronger in CD20-depleted animals than in controls. There was no significant difference in survival between CD20-depleted and control animals. Our data suggest that a deficiency of Ab responses did not markedly affect viral replication or disease progression and that they may be compensated by more robust cellular responses.