Engagement of glycosylphosphatidylinositol-anchored proteins results in enhanced mouse and human invariant natural killer T cell responses

Abstract

Summary Invariant natural killer T (iNKT) cells are a small subset of lymphocytes that recognize glycolipid antigens in the context of CD1d and consequently produce large quantities of pro‐inflammatory and/or anti‐inflammatory cytokines. Several transmembrane glycoproteins have been implicated in the co‐stimulation of iNKT cell responses. However, whether glycosylphosphatidylinositol (GPI)‐anchored proteins can function in this capacity is not known. Here, we demonstrate that antibody‐mediated cross‐linking of the prototype mouse GPI‐anchored protein Thy‐1 (CD90) on the surface of a double‐negative (CD4−CD8−) iNKT cell line leads to cytokine production at both the mRNA and protein levels. In addition, Thy‐1 triggering enhanced cytokine secretion by iNKT cells that were concomitantly stimulated with α‐galactosylceramide (αGC), consistent with a co‐stimulatory role for Thy‐1 in iNKT cell activation. This was also evident when a CD4+ mouse iNKT cell line or primary hepatic NKT cells were stimulated with αGC and/or anti‐Thy‐1 antibody. Cross‐linking Ly‐6A/E, another GPI‐anchored protein, could also boost cytokine secretion by αGC‐stimulated iNKT cells, suggesting that the observed effects reflect a general property of GPI‐anchored proteins. To extend these results from mouse to human cells, we focused on CD55, a GPI‐anchored protein that, unlike Thy‐1, is expressed on human iNKT cells. Cross‐linking CD55 augmented αGC‐induced iNKT cell responses as judged by more vigorous proliferation and higher CD69 expression. Collectively, these findings demonstrate for the first time that GPI‐anchored proteins are able to co‐stimulate CD1d‐restricted, glycolipid‐reactive iNKT cells in both mice and humans.

CD1d‐independent activation of mouse and human iNKT cells by bacterial superantigens

“…Unfractionated hepatic lymphoid mononuclear cells that contain both NKT and conventional T cells were used as a positive control and also mounted a strong cytokine response to both aGC and SEB (Figure 2a). In our hands, the vast majority of hepatic NK1.1 + TCRb + cells are iNKT cells as evidenced by their reactivity with CD1d tetramer, 28 consistent with their cognate responsiveness to aGC (Figure 2a). However, the NK1.1 + TCRb + cell population may also contain a small number of type II or variant NKT cells, a poorly characterized NKT cell subset with a diverse TCRab repertoire and the ability to regulate iNKT cell functions.…”

“…Despite intense investigations on conventional T-cell responses to SAgs, essentially nothing is known about the effect, if any, of SAgs on iNKT cells in humans. To translate our findings from mouse to human cells, we cultured PBMCs from healthy donors (n¼3; two males and one female; age range: [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] in the presence of various SAgs. We chose to examine the expression of the early activation marker CD69 on human CD3 + CD1d tetramer + iNKT cells shortly after SAg challenge (that is, at 4 and 8 h).…”

Testosterone Increases Susceptibility to Amebic Liver Abscess in Mice and Mediates Inhibition of IFNγ Secretion in Natural Killer T Cells

“…Thus, murine NKT cells are subdivided by the presence or absence of the CD4 marker only [23], [55]. In agreement with our observations in mice, the CD4 − CD8 − NKT cell subset in humans exhibits a Th1-biased cytokine profile (IFN γ , MIP-1α and TNFα) [55], [56], [57] while the CD4 + CD8 + NKT cell subset in human is supposed to induce a Th2-type immune response similar to the CD4+NKT cell subset in mice [55], [58]. Although gender differences in the circulating human NKT cell subsets have not been observed, a comparison of the functional NKT cell profiles between males and females revealed higher frequencies of cells producing IFN γ and MIP1-α in males but similar frequencies of cells in both genders producing IL-4 [54].…”

CD1d- and MR1-Restricted T Cells in Sepsis

“…However, i NKT cells are the likely culprits and the early ­triggers of pathology in d -GalN/LPS-prone mice. This is because i NKT cells comprise the vast majority of hepatic NKT cells in mice ( 217 ). Second, when Koide and coworkers injected NC/Nga mice with the i NKT cell superagonist α-GalCer a few hours before the d -GalN/LPS challenge, endogenous IFN-γ production was restored leading to increased expression of inducible nitric oxide synthase (iNOS), appearance of apoptotic cells in the liver, and 100% mortality ( 215 ).…”