Proc. sustained HIV-1 production. Interestingly, T20 and C34 effectively prevent thymocyte depletion in spite of this sustained replication. Apoptosis of both p24? and p24+ thymocytes appears to be Abiraterone Acetate (CB7630) envelope fusion dependent, as T20, but not saquinavir, is usually capable of reducing thymocyte apoptosis. Together, our data support a model whereby pathogenic envelope-dependent fusion contributes to thymocyte depletion in HIV-1-infected thymus, correlated with induction of apoptosis in both p24+ and p24? thymocytes. Contamination with human immunodeficiency computer virus type 1 (HIV-1) is usually characterized by progressive depletion of CD4+ T cells and eventual progression to AIDS. The mechanisms responsible for CD4+ T-cell depletion are still not fully comprehended. While it was initially thought that direct infection of target cells was responsible for T-cell depletion (26, 55), subsequent observations suggested a contribution of indirect or bystander killing of uninfected cells (examined in reference 24). Throughout contamination, less than 1% of peripheral target cells are infected (8, 11), while most apoptotic T cells in lymphoid organs of infected children and simian immunodeficiency computer virus (SIV)-infected macaques are not productively infected (1, 19). Increased bystander cell death during chronic contamination may represent activation-induced cell death consistent Abiraterone Acetate (CB7630) with an immune response to a chronic pathogen (24, 42). Because lack of immune Mouse Monoclonal to CD133 activation in conjunction with high viral loads is usually observed in sooty mangabees that do not develop disease (9, 32, 43), bystander activation likely plays a role in human progression to AIDS. In contrast to chronic infection, acute contamination is usually characterized by massive and quick depletion of CD4+ memory T Abiraterone Acetate (CB7630) cells, particularly in the gut-associated lymphoid tissue, that is usually thought to occur primarily through direct viral contamination and lysis (7, 23, 25, 51, 52). Greater understanding of the mechanisms by which transmitted viruses mediate T-cell depletion during acute contamination will improve our understanding of HIV-1 pathogenesis. In particular, the dynamics and mechanisms of cell depletion in solid lymphoid organs, including the gut, lymph nodes, spleen, and thymus, require further elucidation. A number of in vivo and ex lover vivo organ systems have been developed as models to study HIV-1-induced CD4+ T-cell depletion. These peripheral blood lymphocyte include the SCID-hu, SCID-hu thymus/liver,lymph node organ culture (or tonsil histoculture) and the human fetal thymus-organ culture (HF-TOC). All offer main cell microenvironments that do not require exogenous activation for replication of main HIV-1 isolates (18, 21, 22) and in some cases are refractory to replication by tissue culture-adapted isolates (40, 49). These systems differ from human infection in that they cannot support an adaptive immune response against HIV. Rather, they serve as models for what might happen in lymphoid organs in vivo if innate immunity was the lone defense against viral replication, such as during acute contamination. Evidence from these models has indicated a prominent role for bystander apoptosis (31, 41) and direct viral lysis (22, 33) as mechanisms of T-cell depletion. The thymus is an apoptotic manufacturing plant designed to produce new na?ve T cells and eliminate auto- or nonreactive T cells by apoptosis. It is a target for HIV-1 contamination, and its disruption has been correlated with disease progression in pediatric patients (13, 34, 53). Furthermore, recovery of thymic function after highly active antiretroviral therapy has been correlated with immune recovery (15-17, 36). Thymic sections from HIV-1-infected humans or SIV/SHIV-infected macaques show increased Abiraterone Acetate (CB7630) apoptosis, suggesting that HIV-1 can either directly or indirectly hasten thymocyte depletion (28, 29, 45, 47, 56). A number of studies addressing mechanisms of CD4+ thymocyte death in the thymus organ have indicated that both direct viral lysis and bystander apoptosis occur during thymocyte depletion (5, 6, 30, 48). Whether bystander apoptosis is usually specifically induced by HIV-1 or occurs nonspecifically after the bulk of lysis-induced thymocyte depletion remains a subject of ongoing argument. Herein we characterize the pathogenic mechanisms of an envelope from a rapid progressor (R3A Env).