One of the major impediments of HIV infection is the abnormally high levels of immune activation that contributes to immune dysregulation and impairs viral clearance. While IFNγ secretion is used as a marker of the functional state of T lymphocytes and NK cells, its role in regulating immune responses is poorly understood. We isolated CD8-depleted PBMCs from HIV infected individuals (n=13). We measured proliferation and cytokine production by HIV-specific CD4 T cells stimulated with HIV Gag in the presence of isotype control, anti-IFNγ and/or anti-PD-L1. We performed apoptosis measurements using Annexing-V binding assays. We also determined the modulatory impact of IFNγ on APCs by measuring expression of PD-1 ligands, HLA-DR, HLA-I and IL-12 secretion. Neutralization of IFNγ produced by Gag stimulated CD4 T cells enhanced proliferation (p=0.0161) and reduced apoptosis of HIV-specific CD4 T cells. IFNγ blockade enhanced IL-13 secretion (p=0.0039) but had no effect on IL-2, IL-10 and TNFα levels. IFNγ induced strong up-regulation of PD-L1, HLA-DR and HLA-I on monocytes but not on B, T and NK cells. IFNγ also induced IL-12 secretion by APCs that acted in a positive feedback loop to further enhance IFNγ secretion. Concurrent blockade of IFNγ and PD-L1 led to a more prominent increase in proliferation of HIV-specific CD4 T cells than blockade of individual pathways. These data provide mechanistic insight on the causal role of IFNγ in T-helper dysregulation in HIV infection.
- Copyright © 2013 by The American Association of Immunologists, Inc.