Negative modulation of invariant natural killer T cell responses to glycolipid antigens by p38 MAP kinase

Invariant natural killer T ( i NKT) cells are CD1d-restricted, glycolipid-reactive lymphocytes with potent immunoregulatory characteristics. Although recent years have witnessed intensified interest in i NKT cells, little is known about intracellular signaling pathways that control i NKT cell responses, including those mediated by mitogen-activated protein kinases (MAPKs). We employed selective inhibitors of ERK1/2, JNK and p38 to examine the importance of these MAPKs in i NKT cell responses to the prototype glycolipid antigen α-galactosylceramide (αGC). Activation of DN32.D3 i NKT cells in the presence of PD98059 led to decreased interleukin (IL)-2 production, indicating a role for ERK in mouse i NKT cell responses. In contrast, addition of the JNK inhibitor SP600125 to cultures did not significantly affect cytokine production, suggesting that JNK is not critically needed for i NKT cell responses. Interestingly, selective inhibition of p38 by either SB203580 or SK&F 86002 resulted in augmented IL-2 production by DN32.D3 cells after stimulation with αGC. This was also evident when i NKT cells were stimulated with an anti-CD3 monoclonal antibody thus bypassing the requirement for CD1d-mediated antigen presentation, indicating that p38 inhibition affects signal transduction downstream of i NKT cells' T cell receptors. Primary splenic i NKT cells similarly exhibited enhanced cytokine response to αGC when cultured in the presence of p38 inhibitors. Importantly, in vivo administration of SB203580 resulted in higher IL-4 and interferon-γ secretion in αGC-treated mice. These results demonstrate that MAPKs play distinct signaling roles in i NKT cells and that both in vitro and in vivo i NKT cell responses to glycolipid antigens can be negatively modulated by p38.