Homotypic NK cell-to-cell communication controls cytokine responsiveness of innate immune NK cells

Abstract

While stationary organ cells are in continuous contact with neighboring cells, immune cells circulate throughout the body without an apparent requirement for cell-cell contact to persist in vivo. This study challenges current convention by demonstrating, both in vitro and in vivo, that innate immune NK cells can engage in homotypic NK-to-NK cell interactions for optimal survival, activation, and proliferation. Using a specialized cell-laden microwell approach, we discover that NK cells experiencing constant NK-to-NK contact exhibit a synergistic increase in activation status, cell proliferation, and anti-tumor function in response to IL-2 or IL-15. This effect is dependent on 2B4/CD48 ligation and an active cytoskeleton, resulting in amplification of IL-2 receptor signaling, enhanced CD122/CD132 colocalization, CD25 upregulation, and Stat3 activation. Conversely, ‘orphan' NK cells demonstrate no such synergy and fail to persist. Therefore, our data uncover the existence of homotypic cell-to-cell communication among mobile innate lymphocytes, which promotes functional synergy within the cytokine-rich microenvironment.

Multi-cellular natural killer (NK) cell clusters enhance NK cell activation through localizing IL-2 within the cluster

“…3A). CD132 formed multiple clusters of relatively small sizes, as previously reported22. In sharp contrast, the majority of CD25 was polarized toward one side of the NK cells as a single patch, and ~85% of polarized CD25 (64 out of 75) overlapped with MTOC, indicating polarization of CD25 toward the direction of the MTOC.…”

“…These findings indicate that IL-2 induced convergence of lytic granules can be augmented by homotypic contact-mediated NK-NK interactions, presumably through interactions of activating receptor-ligand pairs co-expressed on the NK cell surfaces. LFA-1, which accumulates at NK-NK contact sites22, was partially responsible for the granule convergence because anti-LFA-1 blocking significantly reduced granule convergence of NK cells in social microwells (Fig. S2 in SI), similar to NK-target interactions29.…”

“…1A)2122. NK cells in a social microwell can exhibit contact-mediated interactions, whereas those in lonesome microwells cannot.…”

“…We employed lymphocyte-laden microwell technologies, which allow precise control of contact-mediated interactions among lymphocytes and quantitative fluorescence imaging of single cells2122. Characterization of phosphorylation, expression and polarization of signaling molecules within multi-cellular clusters of NK cells revealed that IL-2 captured by IL-2R on one NK cell could trigger IL-2R signaling of other surrounding NK cells through intercellular contact.…”

HSV1 MicroRNA Modulation of GPI Anchoring and Downstream Immune Evasion

“…A principal activating NK receptor is NKG2D, which recognizes several stress-induced ligands: MHC class I polypeptide-related sequence A and B (MICA and MICB) and the UL16 binding protein 1-6 (ULBP1-6) (Lanier, 2015), variably expressed by tumor cells and upregulated by cellular stresses, like those that occur during viral infections (Iannello and Raulet, 2013). Additionally, NK cells express several other activating receptors, such as 2B4, which recognizes CD48, a cognate ligand/receptor expressed by other immune cells (Kim et al., 2014b). Other activating NK receptors, such as the natural cytotoxicity receptors (NCRs) NKp30, NKp44, and NKp46, bind mostly viral hemagglutinins and unknown cellular ligands (Koch et al., 2013).…”