Microbial exposure alters HIV-1-induced mucosal CD4(+) T cell death pathways Ex vivo

作者：Steele Amanda K; Lee Eric J; Manuzak Jennifer A; Dillon Stephanie M; Beckham John David; McCarter Martin D; Santiago Mario L^*; Wilson Cara C

来源：Retrovirology, 2014, 11(1): 14.

DOI：10.1186/1742-4690-11-14

• Human Immunodeficiency Virus
• Programmed cell death
• Microbial translocation

Background: Early HIV-1 infection causes massive CD4+ T cell death in the gut and translocation of bacteria into the circulation. However, the programmed cell death (PCD) pathways used by HIV-1 to kill CD4+ T cells in the gut, and the impact of microbial exposure on T cell loss, remain unclear. Understanding mucosal HIV-1 triggered PCD could be advanced by an ex vivo system involving lamina propria mononuclear cells (LPMCs). We therefore modeled the interactions of gut LPMCs, CCR5-tropic HIV-1 and a commensal gut bacterial species, Escherichia coli. In this Lamina Propria Aggregate Culture (LPAC) model, LPMCs were infected with HIV-1(BaL) by spinoculation and cultured in the presence or absence of heat killed E. coli. CD4+ T cell numbers derived from flow cytometry and viable cell counts were reported relative to mock infection. Viable cells were identified by viability dye exclusion (AqVi), and intracellular HIV-1 Gag p24 protein was used to identify infected cells. Annexin V and AqVi were used to identify apoptotic versus necrotic cells. Caspase-1 and Caspase-3 activities were blocked using specific inhibitors YVAD and DEVD, respectively.
Results: CD4+ T cell depletion following HIV-1 infection was reproducibly observed by 6 days post infection (dpi). Depletion at 6 dpi strongly correlated with infection frequency at 4 dpi, was significantly blocked by Efavirenz treatment, and was primarily driven by p24-negative cells that were predominantly necrotic. HIV-1 infection significantly induced CD4+ T-cell intrinsic Caspase-1 activity, whereas Caspase-1 inhibition, but not Caspase-3 inhibition, significantly blocked CD4+ T cell depletion. Exposure to E. coli enhanced HIV-1 infection and CD4+ T depletion, and significantly increased the number of apoptotic p24+ cells. Notably, CD4+ T cell depletion in the presence of E. coli was partially blocked by Caspase-3, but not by Caspase-1 inhibition.
Conclusions: In the LPAC model, HIV-1 induced Caspase-1 mediated pyroptosis in bystander CD4+ T cells, but microbial exposure shifted the PCD mechanism toward apoptosis of productively infected T cells. These results suggest that mucosal CD4+ T cell death pathways may be altered in HIV-infected individuals after gut barrier function is compromised, with potential consequences for mucosal inflammation, viral dissemination and systemic immune activation.

• 出版日期2014-2-4