Natural killer cells (NKs) play an essential role in antiviral immunity; however, their function in Lymph nodes (LN) during chronic HIV/SIV infection is not fully elucidated. LN follicles constitute major reservoir sites for HIV/SIV persistence. Cure strategies could benefit from the characterization of CXCR5+ NK cells able to access/eliminate HIV-reservoirs.
Here we studied the phenotype, distribution and function of CXCR5+ NK cells in the LN of SHIV naïve and chronic SHIV1157ipd3N4-infected (>14 weeks PI) rhesus macaques (RM) and their association with plasma viral RNA levels. Flow cytometry was used for phenotypic analysis, function (IFN-g, TNF-a, CD107a) was assessed by intracellular staining and in vitro target cell killing experiments. Immunohistochemistry was performed to identify the location of NK cells in B cell follicles.
We found that prior to infection, a significant proportion of NK cells (~15%) expressed CXCR5. Following infection, the frequency of CXCR5+ NK cells was significantly higher in chronic SHIV-infected RM. Phenotypically CXCR5+ NK cells express higher levels of FCgRIIa and FCgRIIIa compared to CXCR5– NK cells, which might be important for ADCC function. The CXCR5+ NK cells demonstrated enhanced polyfunctionality with higher production of IFN-g, TNF-a and CD107a when stimulated with mitogen. Immunohistochemistry analysis confirmed the presence of NK cells in LN follicles. Transcriptional profiling (RNA-seq) of sorted CXCR5+ and CXCR5– NK cells from SHIV-infected RM revealed that CXCR5+ NK cells are activated and express increased levels of cytolytic markers (perforin, granzyme-B, granulysin and CD107a), suggesting that these cells have a higher capacity to kill. Gene set enrichment analysis of CXCR5+ cells additionally showed elevated transcripts associated with cell activation, TNF-alpha, interferon signaling and apoptosis. Importantly, the frequency of CXCR5+ NK cells correlated inversely with plasma SHIV viral RNA levels and exhibited a significant negative association with germinal center Tfh cells
Chronic SHIV infection is characterized by accumulation of NK cells within LN follicles and suggest that CXCR5+ NK cells could play an important role in controlling SHIV infection. Cure strategies should focus on inducing these cells for sustained HIV remission