Natural killer (NK) cells play an essential role in antiviral immunity, but knowledge of their function in secondary lymphoid organs is incomplete. Lymph node follicles constitute a major viral reservoir during infections with HIV-1 and simian immunodeficiency virus of macaques (SIVmac). In contrast, during nonpathogenic infection with SIV from African green monkeys (SIVagm), follicles remain generally virus free. We show that NK cells in secondary lymphoid organs from chronically SIVagm-infected African green monkeys (AGMs) were frequently CXCR5 and entered and persisted in lymph node follicles throughout the follow-up (240 d post-infection). These follicles were strongly positive for IL-15, which was primarily presented in its membrane-bound form by follicular dendritic cells. NK cell depletion through treatment with anti-IL-15 monoclonal antibody during chronic SIVagm infection resulted in high viral replication rates in follicles and the T cell zone and increased viral DNA in lymph nodes. Our data suggest that, in nonpathogenic SIV infection, NK cells migrate into follicles and play a major role in viral reservoir control in lymph nodes.

BackgroundMyeloid-derived suppressor cells (MDSC) are a functional myeloid cell subset that includes myeloid cells with immune suppressive properties. The presence of MDSC has been reported in the peripheral blood of patients with several malignant and non-malignant diseases. So far, direct comparison of MDSC across different diseases and Centers is hindered by technical pitfalls and a lack of standardized methodology. To overcome this issue, we formed a network through the COST Action Mye-EUNITER (www.mye-euniter.eu) with the goal to standardize and facilitate the comparative analysis of human circulating MDSC in cancer, inflammation and infection. In this manuscript, we present the results of the multicenter study Mye-EUNITER MDSC Monitoring Initiative, that involved 13 laboratories and compared circulating MDSC subsets across multiple diseases, using a common protocol for the isolation, identification and characterization of these cells.MethodsWe developed, tested, executed and optimized a standard operating procedure for the isolation and immunophenotyping of MDSC using blood from healthy donors. We applied this procedure to the blood of almost 400 patients and controls with different solid tumors and non-malignant diseases. The latter included viral infections such as HIV and hepatitis B virus, but also psoriasis and cardiovascular disorders.ResultsWe observed that the frequency of MDSC in healthy donors varied substantially between centers and was influenced by technical aspects such as the anticoagulant and separation method used. Expansion of polymorphonuclear (PMN)-MDSC exceeded the expansion of monocytic MDSC (M-MDSC) in five out of six solid tumors. PMN-MDSC expansion was more pronounced in cancer compared with infection and inflammation. Programmed death-ligand 1 was primarily expressed in M-MDSC and e-MDSC and was not upregulated as a consequence of disease. LOX-1 expression was confined to PMN-MDSC.ConclusionsThis study provides improved technical protocols and workflows for the multi-center analysis of circulating human MDSC subsets. Application of these workflows revealed a predominant expansion of PMN-MDSC in solid tumors that exceeds expansion in chronic infection and inflammation.

Elevated blood CXCL10/IP-10 levels during primary HIV-1 infection (PHI) were described as an independent marker of rapid disease onset, more robust than peak viremia or CD4 cell nadir. IP-10 enhances the recruitment of CXCR3+ cells, which include major HIV-target cells, raising the question if it promotes the establishment of viral reservoirs. We analyzed data from four cohorts of HIV+ patients, allowing us to study IP-10 levels before infection (Amsterdam cohort), as well as during controlled and uncontrolled viremia (ANRS cohorts). We also addressed IP-10 expression levels with regards to lymphoid tissues (LT) and blood viral reservoirs in patients and non-human primates. Pre-existing elevated IP-10 levels but not sCD63 associated with rapid CD4 T-cell loss upon HIV-1 infection. During PHI, IP-10 levels and to a lesser level IL-18 correlated with cell-associated HIV DNA, while 26 other inflammatory soluble markers did not. IP-10 levels tended to differ between HIV controllers with detectable and undetectable viremia. IP-10 was increased in SIV-exposed aviremic macaques with detectable SIV DNA in tissues. IP-10 mRNA was produced at higher levels in the small intestine than in colon or rectum. Jejunal IP-10+ cells corresponded to numerous small and round CD68neg cells as well as to macrophages. Blood IP-10 response negatively correlated with RORC (Th17 marker) gene expression in the small intestine. CXCR3 expression was higher on memory CD4+ T cells than any other immune cells. CD4 T cells from chronically infected animals expressed extremely high levels of intra-cellular CXCR3 suggesting internalization after ligand recognition. Elevated systemic IP-10 levels before infection associated with rapid disease progression. Systemic IP-10 during PHI correlated with HIV DNA. IP-10 production was regionalized in the intestine during early SIV infection and CD68+ and CD68neg haematopoietic cells in the small intestine appeared to be the major source of IP-10.

An ideal model for HIV-1 research is still unavailable. However, infection of non-human primates (NHP), such as macaques, with Simian Immunodeficiency Virus (SIV) recapitulates most virological, immunological and clinical hallmarks of HIV infection in humans. It has become the most suitable model to study the mechanisms of transmission and physiopathology of HIV/AIDS. On the other hand, natural hosts of SIV, such as African green monkeys and sooty mangabeys that when infected do not progress to AIDS, represent an excellent model to elucidate the mechanisms involved in the capacity of controlling inflammation and disease progression. The use of NHP-SIV models has indeed enriched our knowledge in the fields of: i) viral transmission and viral reservoirs, ii) early immune responses, iii) host cell-virus interactions in tissues, iv) AIDS pathogenesis, v) virulence factors, vi) prevention and vii) drug development. The possibility to control many variables during experimental SIV infection, together with the resemblance between SIV and HIV infections, make the NHP model the most appropriate, so far, for HIV/AIDS research. Nonetheless, some limitations in using these models have to be considered. Alternative models for HIV/AIDS research, such as humanized mice and recombinant forms of HIV-SIV viruses (SHIV) for NHP infection, have been developed. The improvement of SHIV viruses that mimic even better the natural history of HIV infection and of humanized mice that develop a greater variety of human immune cell lineages, is ongoing. None of these models is perfect, but they allow contributing to the progress in managing or preventing HIV infection.

HIV-1/SIVmac infections deeply disturb innate host responses. Most studies have focused on the impact on dendritic cells and NK cells. A few but insufficient data are available on other innate immune cell types, such as neutrophils. It has been shown that innate lymphoid cells are depleted early and irreversibly during SIVmac/HIV-1 infections. Studies in natural hosts of SIV have contributed to pinpoint that early control of inflammation is crucial. In natural hosts, plasmacytoid dendritic cells, myeloid dendritic cells and NK cells are depleted during acute infection but return to normal levels by the end of acute infection. We summarize here the similarities and differences of various types of innate immune responses in natural hosts compared to pathogenic HIV/SIV mac infections.