Requirement of homotypic NK-cell interactions through 2B4(CD244)/CD48 in the generation of NK effector functions

Abstract

IntroductionThe CD2 family of receptors is part of the immunoglobulin (Ig) superfamily, which includes CD2, 2B4 (CD244), CD48, CD58, SLAM (CD150), CS1, CD84, Ly-9, NTBA (SF2000, Ly108), SF2001 (CD2-F10), and BLAME (B-lymphocyte activator macrophage expressed). 1,2 The CD2 family members are expressed predominantly on hematopoietic cells and have been shown to interact with other molecules of the same subfamily or with themselves. SLAM, CD84, CS1, and NTBA are found to be self-ligands and to mediate homophilic interaction. For example, SLAM expressed on activated T cells binds to SLAM on B cells and promotes their activation. 3-5 CD84 on T cells binds to CD84-Ig fusion protein and enhances IFN-␥ secretion on anti-CD3 mAbmediated T-cell crosslinking. 6 CS1 and NTBA on natural killer (NK) cells augment NK cytotoxicity by homophilic interactions. 7,8 Unlike these receptors, there is no evidence for 2B4-or CD2-mediated homophilic interaction. Instead, CD48, expressed widely on hematopoietic cells including T and NK cells, has been identified as a ligand for 2B4 and CD2. Although both 2B4 and CD2 bind to CD48, the affinity of 2B4 to CD48 is 5-to 10-fold higher than that of CD2. 9 Thus, 2B4/CD48 interaction is likely to dominate over CD2/CD48 interaction in cells coexpressing 2B4, CD2, and CD48, such as NK cells. However, in naive T cells, 2B4 is not expressed; thus, the primary receptor for CD48 in such cells appears to be CD2. 10 2B4 was initially identified as an activating receptor. 11-15 However, more recent studies with human NK cells suggest that 2B4 may not itself be a triggering receptor but instead function as a coreceptor for other NK-associated activating receptors such as NKp46. 16 Similarly, ectopic expression of 2B4 in activated mouse CD8 T cells resulted in T-cell receptor (TCR)-dependent augmentation of cytolysis against antigenic targets. 17 These data suggest that the primary role of 2B4 in both T cells and NK cells may be to regulate other receptor/ligand interactions. There is, however, evidence that 2B4 can act as an inhibitory receptor in both humans 18 and mice. 19,20 Our recent studies show that in murine NK cells 2B4 functions as an inhibitory receptor rather than a costimulatory receptor when engaged by CD48-expressing tumor targets. 19 The mechanism by which 2B4 mediates such opposing functions in mice still remains to be determined. Nevertheless, these data strongly 21 shows that 2B4/CD48 interaction among NK cells and NK-T cells exists and regulates cell proliferation. We confirm that 2B4 interaction with CD48 among NK cells is necessary for optimal expansion and reveal that such an interaction is critical for optimal cytolytic activation of NK cells, IFN-␥ secretion, and elimination of tumor cells in vivo. Our data, therefore, reveal a previously unknown mechanism of augmented NK effector functions by homotypic 2B4/CD48 interaction. Materials and methods MiceC57BL/6 mice between 6 and 12 weeks of age were purchased from Frederick Cancer Research and Developmental Center (National Cancer...

Functional role of human NK cell receptor 2B4 (CD244) isoforms

“…2B4 (CD244), belongs to the signaling lymphocyte-activation molecule (SLAM) family of receptors, which includes SLAM (CD150), CD84, NTB-A (Ly-108), lymphocyte antigen 9 (Ly9; CD229), and CD2-subset 1 (CS1) (also termed CRACC or CD319) [7][8][9][10]. 2B4 is expressed by all NK cells, as well as a subset of memory CD8 1 abT cells, gdT cells, basophils, monocytes and eosinophils [11][12][13][14][15].…”

“…NK cell functions are regulated by a dynamic interplay between activating and inhibitory signals transmitted by distinct classes of receptors found on their surface [3,4]. The balance between positivesignaling receptors and negative-signaling receptors ultimately determines the outcome of NK cell-target cell encounters [5,6].2B4 (CD244), belongs to the signaling lymphocyte-activation molecule (SLAM) family of receptors, which includes SLAM (CD150), CD84, NTB-A (Ly-108), lymphocyte antigen 9 (Ly9; CD229), and CD2-subset 1 (CS1) (also termed CRACC or CD319) [7][8][9][10]. 2B4 is expressed by all NK cells, as well as a subset of memory CD8 1 abT cells, gdT cells, basophils, monocytes and eosinophils [11][12][13][14][15].…”

Regulation of 2B4 (CD244)‐mediated NK cell activation by ligand‐induced receptor modulation

“…2B4 can stimulate NK cell cytotoxicity and cytokine production and its activity is controlled by inhibitory receptors [22,23]. The interaction between 2B4 and its ligand CD48 is important for the proliferation of mouse NK and T cells and is necessary for the generation of effector functions in mouse but not human NK cells [24][25][26][27]. 2B4 can also function as a stimulating ligand for NK cells by triggering NK cell-expressed CD48 [28].…”

Homotypic Cell to Cell Cross-talk Among Human Natural Killer Cells Reveals Differential and Overlapping Roles of 2B4 and CD2

“…The preferential role of 2B4 over CD2 in murine NK cells appears to be due to its high affinity interaction with CD48 because 2B4 binds to CD48 with 5-10-fold higher affinity than CD2 (6). Furthermore, murine 2B4 was shown to function as a costimulatory receptor in response to cytokine (IL-2 or IFN-␣) stimulation, via triggering cell to cell cross-talk through binding to CD48 expressed on neighboring NK cells (7). These homotypic interactions via 2B4/CD48 were found to be necessary for optimal expansion, lytic potential, and cytokine secretion in murine NK cells (7).…”

“…Furthermore, murine 2B4 was shown to function as a costimulatory receptor in response to cytokine (IL-2 or IFN-␣) stimulation, via triggering cell to cell cross-talk through binding to CD48 expressed on neighboring NK cells (7). These homotypic interactions via 2B4/CD48 were found to be necessary for optimal expansion, lytic potential, and cytokine secretion in murine NK cells (7). Additionally, murine 2B4 could also function as a co-stimulatory ligand for CD48, capable of generating bidirectional signals (8,9).…”