Differential and Nonredundant Roles of Phospholipase Cγ2 and Phospholipase Cγ1 in the Terminal Maturation of NK Cells

Abstract

NK cells play a central role in mediating innate immune responses. Activation of NK cells results in cytotoxicity, cytokine, and chemokine secretions. In this study, we show that in mice with targeted deletion of phospholipase Cγ (PLCγ)2, one of the key signal transducers, there are profound effects on the development and terminal maturation of NK cells. Lack of PLCγ2 significantly impaired the ability of lineage-committed NK precursor cells to acquire subset-specific Ly49 receptors and thereby terminal maturation of NK cells. Overexpression of isozyme, PLCγ1, in PLCγ2-deficient NK cells resulted in the successful Ly49 acquisition and terminal maturation of the NK cells; however, it could only partially rescue NKG2D-mediated cytotoxicity with no cytokine production. Furthermore, PLCγ2-deficient NK cells failed to mediate antitumor cytotoxicity and inflammatory cytokine production, displaying a generalized hyporesponsiveness. Our results strongly demonstrate that PLCγ1 and PLCγ2 play nonredundant and obligatory roles in NK cell ontogeny and in its effector functions.

Deletion of PI3K-p85α gene impairs lineage commitment, terminal maturation, cytokine generation and cytotoxicity of NK cells

“…28 The total number of lymphocytes in the BM, spleen and liver were comparable between WT and p85a À/À mice as previously reported 20 (data not shown). Lymphocytes were divided into T (CD3 þ NK1.1 À ), NKT (CD3 þ NK1.1 þ ) and NK (CD3 À NK1.1 þ ) cells based on their staining patterns.…”

“…Our previous studies using PLCg2 À/À mice demonstrated a significant reduction in all the Ly49 þ NK subsets, irrespective of their MHC class I ligand preferences. 28 This observation along with our present study indicates that both PLCg2 and p85a are important for subset specifications. Both PLCg2 and PI3K are known to regulate a number of transcription factors.…”

“…51 Analogous to this, lack of p85a could have resulted in a reduced proliferative rate of CD3 À CD122 þ NK1.1 À CD49b À progenitors. Present observations with p85a À/À mice are distinct compared to our previous studies using PLCg2 À/À mice, where we saw a twofold increase in the numbers of p85a regulates cytokine generation in NK cells A Awasthi et al 28 This indicates that p85a and PLCg2 may be involved in the commitment of early NK progenitors.…”

“…16 Our earlier studies have shown that combinations of PMA and Iono were required for the generation of IFN-g from NK cells. 28 However, this combination failed to p85a regulates cytokine generation in NK cells A Awasthi et al rescue IFN-g generation in p85a À/À NK cells. One possible explanation for this observation is the existence of potential requirement of Src kinases that are activated by PMA.…”

Line of attack: NK cell specificity and integration of signals

“…As a result of this multiplicity, only a few molecules have been shown to be required for natural cytotoxicity in mouse knockout models. Phospholipase C (PLC)-γ2 is an important mediator of degranulation, cytotoxicity, and cytokine production [38][39][40]. Pharmacological inhibition of PLC-γ abrogates degranulation, cytotoxicity and cytokine production by human NK cells, in addition to early signals for intracellular calcium mobilization [41].…”