Influence of Xenogeneic β2-Microglobulin on Functional Recognition of H-2Kb by the NK Cell Inhibitory Receptor Ly49C

Abstract

NK cells maintain self-tolerance through expression of inhibitory receptors that bind MHC class I (MHC-I) molecules. MHC-I can exist on the cell surface in several different forms, including “peptide-receptive” or PR-MHC-I that can bind exogenous peptide. PR-MHC-I molecules are short lived and, for H-2Kb, comprise ∼10% of total MHC-I. In the present study, we confirm that signaling through the mouse NK inhibitory receptor Ly49C requires the presence of PR-Kb and that this signaling is prevented when PR-Kb is ablated by pulsing with a peptide that can bind to it with high affinity. Although crystallographic data indicate that Ly49C can engage H-2Kb loaded with high-affinity peptide, our data suggest that this interaction does not generate an inhibitory signal. We also show that no signaling occurs when the PR-Kb complex has mouse β2-microglobulin (β2m) replaced with human β2m, although replacement with bovine β2m has no effect. Furthermore, we show that β2m exchange occurs preferentially in the PR-Kb component of total H-2Kb. These conclusions were reached in studies modulating the sensitivity to lysis of both NK-resistant syngeneic lymphoblasts and NK-sensitive RMA-S tumor cells. We also show, using an in vivo model of lymphocyte recirculation, that engrafted lymphocytes are unable to survive NK attack when otherwise syngeneic lymphocytes express human β2m. These findings suggest a qualitative extension of the “missing self” hypothesis to include NK inhibitory receptors that are restricted to the recognition of unstable forms of MHC-I, thus enabling NK cells to respond more quickly to events that decrease MHC-I synthesis.

HLA-C is necessary for optimal human immunodeficiency virus type 1 infection of human peripheral blood CD4 lymphocytes

“…In addition, some NK receptors recognize peptide-empty MHC molecules (HLA-G and H-2K b ; Benoit et al, 2005;Gonen-Gross et al, 2005), thus supporting the view that open MHC-I conformers can serve as cis-trans recognition structures. Although our results agree with the genomic/epidemiological data to support an important role for HLA-C in HIV-1 infection, the molecular mechanisms of this role remain obscure.…”

Xenogeneic β2-Microglobulin Substitution Alters NK Cell Function

“…The first bona fide assessment of "altered self" examined the role of peptide in NK cell recognition by Ly49 molecules in vitro (45) ϩ NK cells without significantly altering MHC-I expression profiles (29,33,34). From this we concluded that NK cells can distinguish between self-and modified self-H-2K b molecules via Ly49C.…”

“…As well, ␤ 2 m (either mouse or bovine derived) present in vitro or in vivo may be recombining with the Tg H-2K b molecules and thus facilitating transfer. In particular, bovine ␤ 2 m present in the assays may be relevant to our system in that it has previously been shown that bovine ␤ 2 m present in culturing serum can contribute to the formation of a viable interface for Ly49C binding to H-2K b (29). A third possibility is that there is another (unknown) Ly49 molecule that is equally represented in the Ly49C ϩ/Ϫ fractions that can bind with sufficient affinity to H-2K b bound by h-␤ 2 m and can mediate uptake of these hybrid H-2K…”

“…This restrictive effect has been attributed to the formation of novel surface chemistry and shape that is assumed when the MHC-I H chain binds h-␤ 2 m (30, 31), which in turn negatively impacts on the intermolecular association between Ly49 and MHC-I (27, 28, 29 -34). With respect to Ly49C, binding of h-␤ 2 m to H-2K b does not significantly alter the H-2K b expression level or antigenicity as ascertained using a panel of mAb reagents (29,33,34), yet this association renders otherwise syngeneic B6 target cells sensitive to lysis by Ly49C ϩ NK cells (2).…”

“…d and H-2K b , which has been shown to block their respective associations with Ly49A and Ly49C (27)(28)(29). This restrictive effect has been attributed to the formation of novel surface chemistry and shape that is assumed when the MHC-I H chain binds h-␤ 2 m (30, 31), which in turn negatively impacts on the intermolecular association between Ly49 and MHC-I (27, 28, 29 -34).…”