The Case of the Missing Macrophages: Investigating the role of NKR-P1B:Clr-b self-recognition on tissue-resident myeloid cells.

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Innate immune cell functions are regulated through sophisticated systems of pattern-recognition receptors. One example of a receptor system that regulates innate immune responses is the NKR-P1 family of C-type lectin-like receptors, and its binding ligands, the C-type lectin-related (Clr) family of surface proteins. NKR-P1B is an inhibitory member of this receptor family, which recognizes Clr-b, and is expressed on natural killer cells. Using genetically modified mice lacking NKR-P1B expression, we have observed a marked impairment in lung alveolar macrophage (AM) numbers, a completely unexpected phenotype. We have also found the NKR-P1B is expressed on AMs. We now seek to understand how NKR-P1B:Clr-b recognition system regulates lung-resident myeloid immune cell development and function. We have proposed the follow two objectives: 1. Discover the impact of NKR-P1B expression on AMs and DCs. We will fully characterize the functional and phenotypic differences between wild-type and NKR-P1B-deficient lung-resident AM and dendritic cells (DC). Using confocal microscopy, we will analyze lungs of mice at various ages to determine AM distribution and phenotype. We will perform several functional assays, including cytokine release, phagocytosis, and antigen-presenting assays in the presence of NKR-P1B cross-linking antibodies to simulate the effects of NKR-P1B engagement on normal myeloid cell function. Finally, using bone-marrow chimeras to study NKR-P1B-deficient myeloid cells in wild-type environments and vice versa, we will investigate whether NKR-P1B effects on the myeloid cell populations are cell-intrinsic or extrinsic. 2. Discover the mechanism through which NKR-P1B exerts its effects on AMs and DCs. We have observed evidence for impaired metabolic processing in NKR-P1B-deficient AMs. We will compare the metabolic profiles of WT and NKR-P1B-deficient AMs, as well as their transcriptomes obtained by RNA sequence (RNAseq) analysis to determine differentially expressed genes, and the cellular and metabolic pathways that are involved. We will also investigate NKR-P1B interacting and cell signaling partners in macrophages using the proximity-biotinylation BioID system. Understanding myeloid immune cell development and function strengthens our understanding of cells in general. We have fortuitously stumbled into a previously unappreciatedand apparently criticalcomponent of alveolar macrophage biology, and it is our hope that exploring the involvementboth overall role and specific signaling pathwaysof NKR-P1B:Clr-b interactions in these cells will teach us fundamental lessons about myeloid cell development and function.