Neutralization or absence of the interleukin-23 pathway does not compromise immunity to mycobacterial infection.

Interleukin-23 (IL-23), a member of the IL-12 family, is a heterodimeric cytokine that is composed of the p40 subunit of IL-12 plus a unique p19 subunit. IL-23 is critical for autoimmune inflammation, in part due to its stimulation of the proinflammatory cytokine IL-17A. It is less clear, however, if IL-23 is required during the immune response to pathogens. We examined the role of IL-23 during Mycobacterium bovis BCG infection. We found that IL-23 reduces the bacterial burden and promotes granuloma formation when IL-12 is absent. However, IL-23 does not contribute substantially to host resistance when IL-12 is present, as the ability to control bacterial growth and form granulomata is not affected in IL-23p19-deficient mice and mice treated with a specific anti-IL-23p19 antibody. IL-23p19-deficient mice are also able to mount an effective memory response to secondary infection with BCG. While IL-23p19-deficient mice do not produce IL-17A, this cytokine is not necessary for effective control of infection, and antibody blocking of IL-17A in both wild-type and IL-12-deficient mice also has little effect on the bacterial burden. These data suggest that IL-23 by itself does not play an essential role in the protective immune response to BCG infection; however, the presence of IL-23 can partially compensate for the absence of IL-12. Furthermore, neutralization of IL-23 or IL-17A does not increase susceptibility to mycobacterial BCG infection.

IL-23 enhances the inflammatory cell response in Cryptococcus neoformans infection and induces a cytokine pattern distinct from IL-12.

IL-23, a heterodimeric cytokine composed of the p40 subunit of IL-12 and a novel p19 subunit, has been shown to be a key player in models of autoimmune chronic inflammation. To investigate the role of IL-23 in host resistance during chronic fungal infection, wild-type, IL-12- (IL-12p35-/-), IL-23- (IL-23p19-/-), and IL-12/IL-23- (p40-deficient) deficient mice on a C57BL/6 background were infected with Cryptococcus neoformans. Following infection, p40-deficient mice demonstrated higher mortality than IL-12p35-/- mice. Reconstitution of p40-deficient mice with rIL-23 prolonged their survival to levels similar to IL-12p35-/- mice. IL-23p19-/- mice showed a moderately reduced survival time and delayed fungal clearance in the liver. Although IFN-gamma production was similar in wild-type and IL-23p19-/- mice, production of IL-17 was strongly impaired in the latter. IL-23p19-/- mice produced fewer hepatic granulomata relative to organ burden and showed defective recruitment of mononuclear cells to the brain. Moreover, activation of microglia cells and expression of IL-1beta, IL-6, and MCP-1 in the brain was impaired. These results show that IL-23 complements the more dominant role of IL-12 in protection against a chronic fungal infection by an enhanced inflammatory cell response and distinct cytokine regulation.

Polyamides reveal a role for repression in latency within resting T cells of HIV-infected donors.

BACKGROUND: The persistence of human immunodeficiency virus (HIV) type 1 within resting CD4+ T cells poses a daunting therapeutic challenge. Histone deacetylase (HDAC)-1, a chromatin-remodeling enzyme that can mediate gene silencing, is recruited to the HIV-1 long terminal repeat by the host transcription factor LSF. Pyrrole-imidazole polyamides, small molecules that target specific DNA sequences, can access the nucleus of cells and specifically block transcription-factor binding. METHODS: We used polyamides to directly test the role of chromatin remodeling in HIV quiescence in primary resting CD4+ T cells obtained from HIV-infected patients. RESULTS: After exposure to any of 4 different polyamides that specifically block HDAC-1 recruitment by LSF to the HIV promoter, replication-competent HIV was recovered from cultures of resting CD4+ T cells in 6 of 8 HIV-infected patients whose viremia had been suppressed by therapy. In comparison, HIV was not recovered after exposure to control, mismatched polyamides but was recovered from 7 of 8 of these patients' samples after the activation of T cells. CONCLUSIONS: We identify histone deacetylation as a mechanism that can dampen viral expression in infected, activated CD4+ T cells and establish a persistent, quiescent reservoir of HIV infection.

Lipid-drug association enhanced HIV-1 protease inhibitor indinavir localization in lymphoid tissues and viral load reduction: a proof of concept study in HIV-2287-infected macaques.

Analysis of indinavir levels in HIV-positive patients indicated that drug concentrations in lymph node mononuclear cells (LNMCs) were about 25-35% of mononuclear cells in blood. To enhance lymphatic delivery of anti-HIV drugs, a novel drug delivery strategy was designed consisting of lipid-associated indinavir (50-80 nm in diameter) complexes in suspension for subcutaneous (SC) injection. Due to the pH-dependent lipophilicity of indinavir, practically all the drug molecules are incorporated into lipid phase when formulated at pH 7.4 and 5:1 lipid-to-drug (m/m) ratio. At pH 5.5, about 20% of drugs were found in lipid-drug complexes. Effects of lipid association on the time course of plasma indinavir concentrations were determined in macaques (Macaca nemestrina) administered with either soluble or lipid-associated formulation of indinavir (10 mg/kg, SC). Results yielded about a 10-fold reduction in peak plasma concentration and a 6-fold enhancement in terminal half-life (t1/2beta = 12 vs. 2 hours). In addition, indinavir concentrations in both peripheral and visceral lymph nodes were 250-2270% higher than plasma (compared with <35% with soluble lipid-free drug administration in humans). Administration of lipid-associated indinavir (20 mg/kg daily) to HIV-2287-infected macaques (at 30-33 weeks after infection) resulted in significantly reduced viral RNA load and increased CD4 T cell number concentrations. Collectively, these data indicate that lipid association greatly enhances delivery of the anti-HIV drug indinavir to lymph nodes at levels that cannot be achieved with soluble drug, provides significant virus load reduction, and could potentially reverse CD4 T cell depletion due to HIV infection.

Evolutionary indicators of human immunodeficiency virus type 1 reservoirs and compartments.

In vivo virologic compartments are cell types or tissues between which there is a restriction of virus flow, while virologic reservoirs are cell types or tissues in which there is a relative restriction of replication. The distinction between reservoirs and compartments is important because therapies that would be effective against a reservoir may not be effective against viruses produced by a given compartment, and vice versa. For example, the use of cytokines to "flush out" long-lived infected cells in patients on highly active antiretroviral therapy (T. W. Chun, D. Engel, M. M. Berrey, T. Shea, L. Corey, and A. S. Fauci, Proc. Natl. Acad. Sci. USA 95:8869-8873, 1998) may be successful for a latent reservoir but may not impact a compartment in which virus continues to replicate because of poor drug penetration. Here, we suggest phylogenetic criteria to illustrate, define, and differentiate between reservoirs and compartments. We then apply these criteria to the analysis of simulated and actual human immunodeficiency virus type 1 sequence data sets. We report that existing statistical methods work quite well at detecting viral compartments, and we learn from simulations that viral divergence from a calculated most recent common ancestor is a strong predictor of viral reservoirs.

Virus population homogenization following acute human immunodeficiency virus type 1 infection.

Understanding the properties of human immunodeficiency virus type 1 (HIV-1) variants capable of establishing infection is critical to the development of a vaccine against AIDS. Previous studies of men have shown that the HIV-1 env gene is homogeneous early in infection, leading to the suggestion that infection is established by a single transmitted variant. However, we report here that all of eight homosexual men evaluated beginning 3.7 to 9 weeks following onset of symptoms of acute infection harbored diverse virus populations in their blood, with median genetic distances averaging 1.08% in the env C2V5 region and 0.81% in the gag p17 gene. Within another 4.7 to 11 weeks, the variant lineage in env became more homogeneous, while gag sequences continued to diversify. Thus, the homogenization that has been reported to characterize acute infection is actually preceded by the replication of multiple virus variants. This early selective process focuses on viral properties within Env but not Gag p17. Hence, the viral homogeneity observed early in HIV-1 infection results from a selective process that occurs during the establishment of infection.