Cerebrospinal Fluid Biomarkers of Simian Immunodeficiency Virus Encephalitis : CSF Biomarkers of SIV Encephalitis

Antiretroviral therapy has led to increased survival of HIV-infected patients but also increased prevalence of HIV-associated neurocognitive disorders. We previously identified YKL40 as a potential cerebrospinal fluid (CSF) biomarker of lentiviral central nervous system (CNS) disease in HIV-infected patients and in the macaque model of HIV encephalitis. The aim of this study was to define the specificity and sensitivity along with the predictive value of YKL40 as a biomarker of encephalitis and to assess its relationship to CSF viral load. CSF YKL40 and SIV RNA concentrations were analyzed over the course of infection in 19 SIV-infected pigtailed macaques and statistical analyses were performed to evaluate the relationship to encephalitis. Using these relationships, CSF alterations of 31 neuroimmune markers were studied pre-infection, during acute and asymptomatic infection, at the onset of encephalitis, and at necropsy. YKL40 CSF concentrations above 1122 ng/ml were found to be a specific and sensitive biomarker for the presence of encephalitis and were highly correlated with CSF viral load. Macaques that developed encephalitis had evidence of chronic CNS immune activation during early, asymptomatic, and end stages of infection. At the onset of encephalitis, CSF demonstrated a rise of neuroimmune markers associated with macrophage recruitment, activation and interferon response. CSF YKL40 concentration and viral load are valuable biomarkers to define the onset of encephalitis. Chronic CNS immune activation precedes the development of encephalitis while some responses suggest protection from CNS lentiviral disease.

Resistance to simian immunodeficiency virus low dose rectal challenge is associated with higher constitutive TRIM5α expression in PBMC

Background

At least six host-encoded restriction factors (RFs), APOBEC3G, TRIM5α, tetherin, SAMHD1, schlafen 11, and Mx2 have now been shown to inhibit HIV and/or SIV replication in vitro. To determine their role in vivo in the resistance of macaques to mucosally-acquired SIV, we quantified both pre-exposure (basal) and post-exposure mRNA levels of these RFs, Mx1, and IFNγ in PBMC, lymph nodes, and duodenum of rhesus macaques undergoing weekly low dose rectal exposures to the primary isolate, SIV/DeltaB670.

Results

Repetitive challenge divided the monkeys into two groups with respect to their susceptibility to infection: highly susceptible (2–3 challenges, 5 monkeys) and poorly susceptible (≥6 challenges, 3 monkeys). Basal RF and Mx1 expression varied among the three tissues examined, with the lowest expression generally detected in duodenal tissues, and the highest observed in PBMC. The one exception was A3G whose basal expression was greatest in lymph nodes. Importantly, significantly higher basal expression of TRIM5α and Mx1 was observed in PBMC of animals more resistant to mucosal infection. Moreover, individual TRIM5α levels were stable throughout a year prior to infection. Post-exposure induction of these genes was also observed after virus appearance in plasma, with elevated levels in PBMC and duodenum transiently occurring 7–10 days post infection. They did not appear to have an effect on control of viremia. Interestingly, minimal to no induction was observed in the resistant animal that became an elite controller.

Conclusions

These results suggest that constitutively expressed TRIM5α appears to play a greater role in restricting mucosal transmission of SIV than that associated with type I interferon induction following virus entry. Surprisingly, this association was not observed with the other RFs. The higher basal expression of TRIM5α observed in PBMC than in duodenal tissues emphasizes the understated role of the second barrier to systemic infection involving the transport of virus from the mucosal compartment to the blood. Together, these observations provide a strong incentive for a more comprehensive examination of the intrinsic, variable control of constitutive expression of these genes in the sexual transmission of HIV.

Response of simian immunodeficiency virus to the novel nucleoside reverse transcriptase inhibitor 4'-ethynyl-2-fluoro-2'-deoxyadenosine in vitro and in vivo

Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) are essential components in first-line therapy for human immunodeficiency virus (HIV) infection. However, long-term treatment with existing NRTIs can be associated with significant toxic side effects and the emergence of drug-resistant strains. The identification of new NRTIs for the continued management of HIV-infected people therefore is paramount. In this report, we describe the response of a primary isolate of simian immunodeficiency virus (SIV) to 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) both in vitro and in vivo. EFdA was 3 orders of magnitude better than tenofovir (TFV), zidovudine (AZT), and emtricitabine (FTC) in blocking replication of SIV in monkey peripheral blood mononuclear cells (PBMCs) in vitro, and in a preliminary study using two SIV-infected macaques with advanced AIDS, it was highly effective at treating SIV infection and AIDS symptoms in vivo. Both animals had 3- to 4-log decreases in plasma virus burden within 1 week of EFdA therapy (0.4 mg/kg of body weight, delivered subcutaneously twice a day) that eventually became undetectable. Clinical signs of disease (diarrhea, weight loss, and poor activity) also resolved within the first month of treatment. No detectable clinical or pathological signs of drug toxicity were observed within 6 months of continuous therapy. Virus suppression was sustained until drug treatment was discontinued, at which time virus levels rebounded. Although the rebound virus contained the M184V/I mutation in the viral reverse transcriptase, EFdA was fully effective in maintaining suppression of mutant virus throughout the drug treatment period. These results suggest that expanded studies with EFdA are warranted.

Therapeutic DNA vaccine induces broad T cell responses in the gut and sustained protection from viral rebound and AIDS in SIV-infected rhesus macaques

Immunotherapies that induce durable immune control of chronic HIV infection may eliminate the need for life-long dependence on drugs. We investigated a DNA vaccine formulated with a novel genetic adjuvant that stimulates immune responses in the blood and gut for the ability to improve therapy in rhesus macaques chronically infected with SIV. Using the SIV-macaque model for AIDS, we show that epidermal co-delivery of plasmids expressing SIV Gag, RT, Nef and Env, and the mucosal adjuvant, heat-labile E. coli enterotoxin (LT), during antiretroviral therapy (ART) induced a substantial 2-4-log fold reduction in mean virus burden in both the gut and blood when compared to unvaccinated controls and provided durable protection from viral rebound and disease progression after the drug was discontinued. This effect was associated with significant increases in IFN-γ T cell responses in both the blood and gut and SIV-specific CD8+ T cells with dual TNF-α and cytolytic effector functions in the blood. Importantly, a broader specificity in the T cell response seen in the gut, but not the blood, significantly correlated with a reduction in virus production in mucosal tissues and a lower virus burden in plasma. We conclude that immunizing with vaccines that induce immune responses in mucosal gut tissue could reduce residual viral reservoirs during drug therapy and improve long-term treatment of HIV infection in humans.

YKL-40, a marker of simian immunodeficiency virus encephalitis, modulates the biological activity of basic fibroblast growth factor

Human immunodeficiency virus encephalitis causes dementia in acquired immune deficiency syndrome patients. Using proteomic analysis of postmortem cerebrospinal fluid (CSF) and brain tissue from the simian immunodeficiency virus primate model, we demonstrate here a specific increase in YKL-40 that was tightly associated with lentiviral encephalitis. Longitudinal analysis of CSF from simian immunodeficiency virus-infected pigtailed macaques showed an increase in YKL-40 concentration 2 to 8 weeks before death from encephalitis. This increase in YKL-40 correlated with an increase in CSF viral load; it may therefore represent a biomarker for the development of encephalitis. Analysis of banked human CSF from human immunodeficiency virus-infected patients also demonstrated a correlation between YKL-40 concentration and CSF viral load. In vitro studies demonstrated increased YKL-40 expression and secretion by macrophages and microglia but not by neurons or astrocytes. We found that YKL40 displaced extracellular matrix-bound basic fibroblast growth factor (bFGF) as well as inhibited the mitogenic activity of both fibroblast growth factor receptor 1-expressing BaF3 cells and bFGF-induced axonal branching in hippocampal cultures. Taken together, these findings demonstrate that during lentiviral encephalitis, YKL-40 may interfere with the biological activity of bFGF and potentially of other heparin-binding growth factors and chemokines that can affect neuronal function or survival.

Schistosome-induced pathology is exacerbated and Th2 polarization is enhanced during pregnancy

THE AIM of this study was to investigate the immunopathological impact of pregnancy on an ongoing experimental schistosomiasis infection.

MATERIALS AND METHODS

Female BALB/c mice were randomly divided into three groups (A, B and C) of 15 animals each. The mice in Groups A and B were infected with 40 S. mansoni cercariae, percutaneously. Six weeks post-infection, the mice in Groups B and C (schistosome-naive controls) were mated. Schistosome-induced morbidity and cytokine recall responses were subsequently evaluated at weeks 7 and 8 post-infection.

RESULTS

Hepatic and pulmonary lesions resulting from trapped schistosome eggs were more frequent and more severe in Group B mice than in Group A mice. Group C mice had suppressed mitogen-stimulated interleukin 4 (IL-4) but maintained high intereferon gamma (IFN-gamma) responses. In contrast, Group A mice had elevated mitogen- and parasite-specific IL-4 but muted IFN-gamma responses. Group B mice had an early (week 7) high IL-4 response, even higher than in group A mice.

CONCLUSION

Taken together the data suggest that pregnancy exacerbates schistosome-induced morbidity, probably through up-regulation of parasite-specific IL-4.

Schistosoma mansoni: development and modulation of the granuloma after or multiple exposures in the baboon (Papio cynocephalus anubis)

The ability of the host to modulate the granulomatous response around ova trapped in tissues determines the severity of disease to schistosome infections. Multiple factors may affect this modulation such as age, prior sensitization, history of treatment, and exposure. The present study examines the effect of different patterns of exposure on the sequential development and modulation of granuloma in juvenile Kenyan baboons (Papio cynocephalus anubis) after receiving either a single infection (SI) of 1500 Schistosoma mansoni cercariae or multiple infections (MI) of 150 cercariae, once a week for 10 weeks. Prior to sacrifice at 17 weeks postinfection (p.i.), liver biopsies were obtained at Weeks 0, 6, 9, and 13. SI animals experienced more prolonged dysentery and greater weight loss compared to MI animals. Peak hepatic granuloma size (mean 355 +/- 65.5 microns diameter), the maximum percentage of eosinophils in the granuloma (61%), and severity of disease occurred at 6 weeks in SI animals. Peak granuloma size and pathology did not appear until Week 9 in the MI animals (mean 317.7 +/- 67.3 microns diameter). Granuloma size, tissue eosinophilia, and gross pathology diminished by Week 13 p.i. and were virtually absent in both groups by Week 17. The decrease in granuloma size, pathology, and clinical illness resolved more rapidly in the MI baboons. Singly infected baboons were more susceptible to infection (83 +/- 12% of cercariae developed into adult worms) compared to MI baboons (67 +/- 7%, P < 0.01). Eggs recovered from tissues at necropsy were primarily confined to the large intestine (85% of total egg recovered), followed by liver (10%) and small intestine (5%). Significantly more eggs were recovered from MI compared to SI animals, indicating a higher fecundity of female worms in the MI baboons. These date demonstrate that granulomatous responses develop more slowly and modulate more rapidly with repeated infection compared to a single heavy infection and suggest the type of exposure may affect the pathologic response to infection.