Immune dysregulation in HIV-1 infected lymphoid tissue

Abstract

Lymphoid compartments are major sites for HIV-1 replication. We evaluated cytokines, chemokines and immunological effector function at the single cell level in lymphoid tissues in chronically HIV-1 infected patients. HIV-1 infected lymphoid tissue was characterized by an extensive proinflammatory activation (IL-1alpha, IL-1beta and IL-12) and vigorous Th 1 type cytokine expression (IL-2 and IFN-gamma) while Th2 cytokines remained low (IL-4 and IL-10). Treatment with highly active anti-retroviral therapy (HAART) resulted in a significant reduction of proinflammatory as well as of Th 1 type of cytokine expression in lymphoid tissue. However, the pool of HIV-1 DNA containing cells (1 5%) remained virtually unchanged even after more than one year of HAART while the initial 3-8-fold increase of CD8+ T cells was normalized.

We hypothesized that lack of elimination of HIV-1 infected cells was due to impaired cytolytic effector function in activated CD8+ T cells that normally are mediated by either Fas-L/Fas interaction or perforin/granzyme A (grA). CD8+ T cells in HIV-1 infected lymphoid tissue were found to have upregulated Fas-L and grA expression while perforin expression was not concomitantly induced. This was however not true for CD8+ T cells obtained from acutely EBV infected patients, which instead showed upregulation of both perforin and grA expression.

Our data indicated a defective cytolytic activity in CD8+ T cells at local sites of HIV-1 replication within lymphoid tissue. To elucidate the molecular mechanism involved in inhibition of perforin expression in HIV- 1 infection, we initiated short term in vitro cultures using freshly isolated peripheral blood cells from HIV-1 seronegative donors. Exogenous addition of Nef protein was found to mediate downregulation of perforin in CD8+ T cells. Sequence alignments and molecular modeling of different Nef proteins suggested that the so-called disordered loop corresponding to residues 148-178 was a likely contributor to the observed Nef-mediated downregulation of perforin expression. Macaques infected with a nef-deleted virus displayed high perforin expression within lymphoid tissues in contrast to macaques infected with the wild-type virus, which suggested a role for Nef as perforin modulator in vivo.

Furthermore, cytokine mediated regulation of chemokine receptor expression (CCR5CXCR4) was studied in placenta tissue from transmitting (TT) and non-transmitting (TNT) HIV- 1 infected women. We found upregulation of CCR5 combined with IL-2 expression both at the protein and mRNA level in placenta from TT women. This was associated with an increase in the number of gag-pol mRNA expressing cells. In contrast, the placenta from TNT women was characterised by upregulation of Th2 type (IL-4, IL- 10) cytokine expression. We found an association between Th2 type of cytokine (IL-4) expression and Leukemia Inhibitor Factor (LIF) production in placenta from TNT tissue while LIF expression was low in placenta from TT women. Therefore, we investigated whether LIF secretion may play a role in HIV-1 inhibition. LIF inhibited HIV-1 replication in a co-receptor independent manner. This inhibition was dependent upon the expression of LIF-R beta (gp 13 0) on the surface of HIV-1 susceptible cells. The identification of LIF as an inhibitor of HIV-1 replication may lead to the development of a novel anti-retroviral treatment.