CD4+ T-cell dysfunctions through the impaired lipid rafts ameliorate concanavalin A-induced hepatitis in sphingomyelin synthase 1-knockout mice

Membrane microdomains consisting of sphingomyelin (SM) and cholesterol appear to be important for signal transduction in T-cell activation. The present study was designed to elucidate the role of membrane SM in vivo and in vitro using sphingomyelin synthase 1 (SMS1) knock out (SMS1 2/2 ) mice and Concanavalin A (ConA)-induced hepatitis. After establishing SMS1 2/2 mice, we investigated CD41 T-cell functions including proliferation, cytokine production and signal transduction in vivo. We also examined severity of hepatitis, cytokine production in serum and liver after ConA injection at a dose of 20 mg kg 21 . CD41 T cells from SMS1 2/2 mice showed severe deficiency of membrane SM and several profound defects compared with wild-type controls as follows: (i) cellular proliferation and production of IL-2 and IFN-g by co-cross-linking of CD3 and CD4; (ii) tyrosine phosphorylation of LAT and its association with ZAP-70; (iii) clustering and co-localization of TCR with lipid rafts. Consistent with these impaired CD41 T-cell functions in vitro, SMS1 2/2 mice showed decreased serum levels of IL-6 and IFN-g by ConA injection, which renders SMS1 2/2 mice less sensitive to ConAinduced hepatitis. These results indicated that the deficiency of membrane SM caused the CD41 T-cell dysfunction through impaired lipid raft function contributed to protection of ConA-induced liver injury, suggesting that the membrane SM is critical for full T-cell activation both in vitro and in vivo.