Abstract Anti-viral CD8+ T-cell responses become impaired in HIV infection in part due to decreased T-cell survival, function and memory cell development; aspects mediated largely by interleukin-7 (IL-7). In progressive HIV infection, decreased T-cell expression of the IL-7 receptor α (CD127) and impaired IL-7 signalling, despite increased IL-7 production, may contribute to failing T-cell activity. Here we examine the effects of IL-7 on a panel of signalling pathways and investigates how IL-7 signalling pathways are associated with IL-7-related activities in CD8+ T-cells. Low concentrations of IL-7 (10 pg/ml) are capable of inducing maximum activation of the Jak-STAT and PI3K signalling pathways, while higher concentrations (500-1000 pg/ml) were required to induce Bcl-2 production and glucose uptake. Even higher concentrations of IL-7 (10,000 pg/ml) were needed to induce cell proliferation and perforin release. Inhibition of Jak activation reduced IL-7-induced Bcl-2, perforin production and proliferation. The activation of intracellular signalling pathways by IL-7 in human CD8+ T-cells and how they are associated with IL-7-induced functions has been extensively studied. Furthermore, the kinetic and optimal concentrations of IL-7 required for the induction of these functional outcomes suggest a complex control of IL-7-associated functions. This may provide insight in immune restoration therapies in HIV infection, where IL-7 signalling and functions are impaired.
HIV infection elicits defects in CD4 T-cell homeostasis in both a quantitative and qualitative manner. Interleukin-7 (IL-7) is essential to T-cell homeostasis and several groups have shown reduced levels of the IL-7 receptor alpha-chain (CD127) on both CD4 and CD8 T-cells in viremic HIV+ patients. We have shown previously that soluble HIV Tat protein specifically down regulates cell surface expression of CD127 on human CD8 T-cells in a paracrine fashion. The effects of Tat on CD127 expression in CD4 T-cells has yet to be described. To explore this effect, CD4 T-cells were isolated from healthy individuals and expression levels of CD127 were examined on cells incubated in media alone or treated with Tat protein. We show here that, similar to CD8 T-cells, the HIV-1 Tat protein specifically down regulates CD127 on primary human CD4 T-cells and directs the receptor to the proteasome for degradation. Down regulation of CD127 in response to Tat was seen on both memory and naive CD4 T-cell subsets and was blocked using either heparin or anti-Tat antibodies. Tat did not induce apoptosis in cultured primary CD4 T-cells over 72 hours as determined by Annexin V and PI staining. Pre-incubation of CD4 T-cells with HIV-1 Tat protein did however reduce the ability of IL-7 to up regulate Bcl-2 expression. Similar to exogenous Tat, endogenously expressed HIV Tat protein also suppressed CD127 expression on primary CD4 T-cells. In view of the important role IL-7 plays in lymphocyte proliferation, homeostasis and survival, down regulation of CD127 by Tat likely plays a central role in immune dysregulation and CD4 T-cell decline. Understanding this effect could lead to new approaches to mitigate the CD4 T-cell loss evident in HIV infection.
BACkGROUND:The C-type lectin CD161 is expressed by CD4+ and CD8+ T cells sharing conserved transcriptional and functional signature.CD4+ T cells with type-17 profiles derived from CD161+ precursors and CD161-expressing CD8+ T cells share the same differentiation profile and include the unique anti-bacterial CD161++ mucosal-associated invariant T cells (MAIT) expressing invariant TCR Vα7.2.During HIV infection, circulating cells harbouring the signature of CD161+ cells are impaired in blood and mucosal compartments.In the female genital tract (FGT), portal of entry for HIV infection, the pattern of CD161 expression on CD4+ and CD8+ subsets and how HIV infection impacts these compartments remain unknown.Here, we explore these questions by characterizing CD161-expressing cells in the FGT of chronically HIVinfected (n=16), HIV-negative newly practising sex work (n=36) and highly HIV-exposed seronegative (HESN) (n=33) female sex workers (FSW) from Nairobi, Kenya.RESULTS: When compared to blood, CD161+CD4+ T cells were enriched in the FGT of HIV-negatives.CD161+CD8+ T cells were also enriched in the FGT of new FSW but not in HESN.Circulating and cervical CD161-expressing cells harboured a more activated profile with tissue-homing properties (CD69, CCR5 and β7) on both CD4+ and CD8+ subsets.The CD161++ subsets included MAIT.Stimulated CD161++ and CD161+CD8+ cells expressed IL-22 at higher frequency than CD161-cells.Expression of IL-17A and IL-22 was enriched in FGT, but independently of CD161 expression in cervical CD4+ cells.CD161++CD8+ T cells were depleted in HIV-positives compared to new FSW in both blood and cervix, but depletion of CD161+CD8+ subset was only observed in cervix.CONCLUSION: Impairment of the IL-17A/IL-22-enriched CD161+ +CD8+ and CD161+ subsets was observed for the first time in the FGT of HIV-infected FSW.Also, the absence of cervical enrichment of CD161+CD8+ cells in HESN agrees with a protective reduction of cervical inflammation.In contrast to blood, CD161 expression did not efficiently describe type-17 CD4+ T cells in the FGT.The FGT unique environment may importantly impact T cells plasticity promoting Th17 differentiation independently of CD161 expression.
BACkGROUND:The C-type lectin CD161 is expressed by CD4+ and CD8+ T cells sharing conserved transcriptional and functional signature.CD4+ T cells with type-17 profiles derived from CD161+ precursors and CD161-expressing CD8+ T cells share the same differentiation profile and include the unique anti-bacterial CD161++ mucosal-associated invariant T cells (MAIT) expressing invariant TCR Vα7.2.During HIV infection, circulating cells harbouring the signature of CD161+ cells are impaired in blood and mucosal compartments.In the female genital tract (FGT), portal of entry for HIV infection, the pattern of CD161 expression on CD4+ and CD8+ subsets and how HIV infection impacts these compartments remain unknown.Here, we explore these questions by characterizing CD161-expressing cells in the FGT of chronically HIVinfected (n=16), HIV-negative newly practising sex work (n=36) and highly HIV-exposed seronegative (HESN) (n=33) female sex workers (FSW) from Nairobi, Kenya.RESULTS: When compared to blood, CD161+CD4+ T cells were enriched in the FGT of HIV-negatives.CD161+CD8+ T cells were also enriched in the FGT of new FSW but not in HESN.Circulating and cervical CD161-expressing cells harboured a more activated profile with tissue-homing properties (CD69, CCR5 and β7) on both CD4+ and CD8+ subsets.The CD161++ subsets included MAIT.Stimulated CD161++ and CD161+CD8+ cells expressed IL-22 at higher frequency than CD161-cells.Expression of IL-17A and IL-22 was enriched in FGT, but independently of CD161 expression in cervical CD4+ cells.CD161++CD8+ T cells were depleted in HIV-positives compared to new FSW in both blood and cervix, but depletion of CD161+CD8+ subset was only observed in cervix.CONCLUSION: Impairment of the IL-17A/IL-22-enriched CD161+ +CD8+ and CD161+ subsets was observed for the first time in the FGT of HIV-infected FSW.Also, the absence of cervical enrichment of CD161+CD8+ cells in HESN agrees with a protective reduction of cervical inflammation.In contrast to blood, CD161 expression did not efficiently describe type-17 CD4+ T cells in the FGT.The FGT unique environment may importantly impact T cells plasticity promoting Th17 differentiation independently of CD161 expression.
Interleukin (IL)-7 is an essential nonredundant cytokine, and throughout the lifespan of a T-cell signaling via the IL-7 receptor influences cell survival, proliferation and differentiation. It is therefore no surprise that expression of the IL-7 receptor alpha-chain (CD127) is tightly regulated. We have previously shown that IL-7 downregulates expression of CD127 at the cell surface and now elucidate the kinetics of that suppression and demonstrate that IL-7 downregulates CD127 transcripts and surface protein in primary human CD8 T cells by two separate pathways. We show that IL-7 induces the initial reduction in cell-surface CD127 protein independent of transcriptional suppression, which is delayed by 40-60 min. Although IL-7-mediated downregulation of CD127 transcripts is dependent on Janus kinase (JAK)/STAT5, the early downregulation of surface CD127 protein is independent of JAK activity. The data further illustrate that low levels of IL-7 induce smaller and transient decreases in CD127 transcripts and surface protein, whereas higher concentrations induce more profound and sustained suppression. Such flexibility in receptor expression likely allows for fine-tuned immune responses in human CD8 T cells in different microenvironments and in response to different immunological challenges.
