Kollnberger, S. | bioRxiv Science

bioRxiv2024

NKG2A-mediated immune modulation of natural killer cells by Staphylococcus aureus

Natural killer (NK) cells are specialized lymphocytes that help protect against viruses and cancer. However, in the context of bacterial infections, NK cells can be harmful, rather than protective. Such immune pathogenesis by NK cells has been linked to the over-production of pro-inflammatory cytokines like interferon-{gamma} (IFN-{gamma}). In this context, IFN-{gamma}-deficient mice display increased survival rates in response to Staphylococcus aureus (S. aureus), which causes life-threatening, invasive systemic infections with high mortality rates in humans. However, little is known about how NK cells respond to S. aureus in humans. In this study, we found that the peripheral blood of patients with bloodstream S. aureus infection was enriched for NKG2A+ NK cells with greater cytokine producing capacity, compared to those hospitalized with Escherichia coli bloodstream infections. As a possible mechanistic cause, superantigens from S. aureus promoted the expansion of CD57- NKG2A+ NK cells which produced IFN-{gamma} through an IL-12-independent mechanism and exhibited reduced levels of CD16 compared to unstimulated NK cells. These data suggest that S. aureus bloodstream infection in humans promotes a phenotypic shift towards NKG2A+ NK cells with greater IFN-{gamma} producing capacity, providing a plausible way to promote inflammation-driven disease pathogenesis. AUTHOR SUMMARYNatural Killer (NK) cells are specialized immune cells that provide crucial defence against viruses but can also respond to bacterial infections, especially in humans. During bloodstream infection by Staphylococcus aureus, a Gram-positive bacterial pathogen that causes life-threatening infections in humans, NK cells may actually be harmful, rather than protective, to the host. However, very little is known about the NK cell response to invasive Staphylococcus aureus infections in humans. Here, we show that human patients with bloodstream Staphylococcus aureus, but not Escherichia coli, infections have an increased frequency of NK cells with increased pro-inflammatory capacity. Furthermore, we show that toxins produced by Staphylococcus aureus, which help the bacteria evade the protective effects of T cells the immune system ("superantigens"), promoted the expansion of these pro-inflammatory NK cells, providing a possible mechanistic cause for their increased presence in patients with bloodstream Staphylococcus aureus infections. Collectively, these results suggest that Staphylococcus aureus infection triggers phenotypic and functional changes in NK cells that provide a plausible way to promote inflammation-driven disease pathogenesis

immunology↗

bioRxiv2023

ADAM17 targeting by human cytomegalovirus remodels the cell surface proteome to simultaneously regulate multiple immune pathways

Human cytomegalovirus (HCMV) is a major human pathogen whose life-long persistence is enabled by its remarkable capacity to systematically subvert host immune defences. In exploring the finding that HCMV infection upregulates tumor necrosis factor receptor 2 (TNFR2), a ligand for the pro-inflammatory anti-viral cytokine TNFa, we discovered the underlying mechanism was due to targeting of the protease, A Disintegrin And Metalloproteinase 17 (ADAM17). ADAM17 is the prototype sheddase, a family of proteases that cleaves other membrane-bound proteins to release biologically active ectodomains into the supernatant. HCMV impaired ADAM17 surface expression through the action of two virally-encoded proteins in its UL/b region, UL148 and UL148D. Proteomic plasma membrane profiling of cells infected with a HCMV double deletion mutant for UL148 and UL148D with restored ADAM17 expression, combined with ADAM17 functional blockade, showed that HCMV stabilized the surface expression of 114 proteins (p<0.05) in an ADAM17-dependent fashion. These included known substrates of ADAM17 with established immunological functions such as TNFR2 and Jagged1, but also numerous novel host and viral targets, such as Nectin1, UL8 and UL144. Regulation of TNF-induced cytokine responses and NK inhibition during HCMV infection were dependent on this impairment of ADAM17. We therefore identify a viral immunoregulatory mechanism in which targeting a single sheddase enables broad regulation of multiple critical surface receptors, revealing a paradigm for viral-encoded immunomodulation. Significance statementHuman cytomegalovirus (HCMV) is an important pathogen, being the commonest infectious cause of brain damage to babies and the primary reason for hospital readmissions in transplant recipients. Even though HCMV induces the strongest immune responses by any human pathogen, it evades host defences and persists for life. This study describes a novel immunoregulatory strategy through which HCMV modulates multiple immune pathways simultaneously, by targeting a single host protein. HCMV UL148 and UL148D impair the maturation of the sheddase, A Disintegrin And Metalloproteinase 17, profoundly altering surface expression of numerous immunoregulatory proteins. This is the first description of viral genes targeting this pathway. Our findings may be relevant for future viral therapies and understanding the impact of HCMV in developmental biology.

microbiology↗