Influence of Self-MHC Class I Recognition on the Dynamics of NK Cell Responses to Cytomegalovirus Infection

ITAM-based receptors in natural killer cells

The ability of cells of the immune system to acquire features such as increased longevity and enhanced secondary responses was long thought to be restricted to cells of the adaptive immune system. Natural killer (NK) cells have challenged this notion by demonstrating that they can also gain adaptive features. This has been observed in both humans and mice during infection with cytomegalovirus (CMV). The generation of adaptive NK cells requires antigen-specific recognition of virally infected cells through stimulatory NK receptors. These receptors lack the ability to signal on their own and rather rely on adaptor molecules that contain ITAMs for driving signals. Here, we highlight our understanding of how these receptors influence the production of adaptive NK cells and propose areas in the field that merit further investigation.

CD90 is not constitutively expressed in functional innate lymphoid cells

Huge progress has been made in understanding the biology of innate lymphoid cells (ILC) by adopting several well-known concepts in T cell biology. As such, flow cytometry gating strategies and markers, such as CD90, have been applied to indentify ILC. Here, we report that most non-NK intestinal ILC have a high expression of CD90 as expected, but surprisingly a sub-population of cells exhibit low or even no expression of this marker. CD90-negative and CD90-low CD127+ ILC were present amongst all ILC subsets in the gut. The frequency of CD90-negative and CD90-low CD127+ ILC was dependent on stimulatory cues in vitro and enhanced by dysbiosis in vivo. CD90-negative and CD90-low CD127+ ILC were a potential source of IL-13, IFNγ and IL-17A at steady state and upon dysbiosis- and dextran sulphate sodium-elicited colitis. Hence, this study reveals that, contrary to expectations, CD90 is not constitutively expressed by functional ILC in the gut.

The CD16 and CD32b Fc-gamma receptors regulate antibody-mediated responses in mouse natural killer cells

Natural killer (NK) cells are innate lymphocytes capable of mediating immune responses without prior sensitization. NK cells express Fc-gamma receptors (FcγRs) that engage the Fc region of IgG. Studies investigating the role of FcγRs on mouse NK cells have been limited due to lack specific reagents. In this study, we characterize the expression and biological consequences of activating mouse NK cells through their FcγRs. We demonstrate that most NK cells express the activating CD16 receptor, and a subset of NK cells also expresses the inhibitory CD32b receptor. Critically, these FcγRs are functional on mouse NK cells and can modulate antibody-mediated responses. We also characterized mice with conditional knockout alleles of Fcgr3 (CD16) or Fcgr2b (CD32b) in the NK and innate lymphoid cell (ILC) lineage. NK cells in these mice did not reveal any developmental defects and were responsive to cross-linking activating NK receptors, cytokine stimulation, and killing of YAC-1 targets. Importantly, CD16-deficient NK cells failed to induce antibody-directed cellular cytotoxicity of antibody-coated B-cell lymphomas in in vitro assays. In addition, we demonstrate the important role of CD16 on NK cells using an in vivo model of cancer immunotherapy using anti-CD20 antibody treatment of B-cell lymphomas.