| Lipid rafts are vital signaling platforms for the function of numerous immune cells including CD8+ T cells. Critical molecules for mediating TCR signaling, such as the src kinases Ick and fyn, can be found within lipid rafts. In addition, lipid rafts have been observed to provide a doorway for entry of various pathogens or toxins, such as cholera toxin, into the cell. Here we examine signaling, mediated through lipid rafts, that occurs in differentially primed T cells in response to viral peptide or cholera toxin subunit B (CTxB). Splenocytes from P14 TCR transgenic mice were primed with differing concentrations of 3 altered peptide ligands, C9M, Y4AC9M and A3 of the LCMV peptide p33. Agonists C9M and Y4AC9M were able to efficiently prime naive CD8+ T cells to exhibit proliferative and cytotoxic function and cytokine secretion at both high and low concentrations of peptide, whereas Δ3 priming required high concentration of peptide. MHC stabilization and relative affinity TCR-tetramer binding assays indicated that the difference in function elicited was due to differences in binding between the peptides and the TCR, but not MHC. Fyn and lck association in lipid rafts correlated with cytotoxic function, as did the aggregation of lipid rafts at the site of target - CD8+ T cell contact. Priming naive P14 CD8 + T cells to become Tc1 or Tc2 through the use of C9M peptide and either IL-12 or IL-4 respectively, resulted in an increase in apoptosis in Tc1 and not in Tc2 in response to incubation with CTxB endotoxin. This increase in apoptosis was a result of increased phosphorylation of active JNK and caspases. Results obtained using CTxB reconcile the observations that CTxB conjugated to antigen elicit a type 2 inflammatory response and that in vitro CTxB induced apoptosis in CD8+, but not CD4 + T cells, by demonstrating that specifically Tc1 undergo apoptosis after incubation with CTxB. Overall these data indicate that the manner in which naïve CD8+ T cells were primed profoundly affected lipid raft maturation and activity in response to external stimuli such as viral antigen or endotoxin. |
