Recently, a novel innate immune cell subset termed natural killer-like B (NKB) cells was identified in mice that rapidly responded to microbial infection and primed the innate antiviral response. Despite a critical role for innate immunity in blocking or limiting viral transmission and disease, the presence and role of NKB in primate HIV/SIV infections is completely unknown.
To identify NKB in primates, up to 18-color polychromatic flow cytometry was used for phenotypic and functional assays. NKB were identified in both rhesus macaques and human samples by flow cytometry excluding lineage markers (CD3–CD14–CD127–) and then positive boolean gating of CD20, NKG2A/C and/or NKp46.
NKB were found at similar frequencies in the circulation of humans (n = 20) and rhesus macaques (n = 12) (range, 0.01 to 0.2% of total lymphocytes) and were systemically distributed at similar frequencies in tonsil, mesenteric and peripheral lymph nodes, colon, and jejunum. NKB were notably enriched in spleen (median, 0.4% of lymphocytes) but frequencies were not altered in any tissue following HIV/SIV infections, and not influenced by ART status. Interestingly, NKB uniquely and uniformly expressed high levels of IgA regardless of tissue, but demonstrated increased IgM and IgG in HIV-infected patients and SIV-infected macaques, which could suggest class-switching or mobilization of de novo cells. NKB also upregulated CD40, HLA-DR, CD16 and NKp46 during infection – highly suggestive of virus-induced activation. Work from our lab and others have shown NKB production of IFN-γ, IL-12, and IL-18, but we found only low-to-moderate expression of granzyme B, and NKB were negative for perforin and had low evidence of cytolytic potential.
These results demonstrate the first conclusive evidence of for systemic NKB in rhesus macaques and humans, and demonstrate their significant perturbation during HIV/SIV infections. Although the full functional niche of this subset is unknown, our preliminary evidence suggests they may be most closely related to other innate B cell lineages (B1). Regardless, their systemic distribution, particularly accumulation in mucosal tissues and secondary lymphoid organs, as well as strikingly high expression of IgA could make these novel cells unique targets for future HIV immunotherapeutics or vaccine strategies.