Orally Tolerized T Cells Can Form Conjugates with APCs but Are Defective in Immunological Synapse Formation

Abstract

Oral tolerance is systemic immune hyporesponsiveness induced by the oral administration of soluble Ags. Hyporesponsiveness of Ag-specific CD4 T cells is responsible for this phenomenon. However, the molecular mechanisms underlying the hyporesponsive state of these T cells are not fully understood. In the present study, we investigated the ability of orally tolerized T cells to form conjugates with Ag-bearing APCs and to translocate TCR, protein kinase C-theta (PKC-theta), and lipid rafts into the interface between T cells and APCs. Orally tolerized T cells were prepared from the spleens of OVA-fed DO11.10 mice. Interestingly, the orally tolerized T cells did not show any impairment in the formation of conjugates with APCs. The conjugates were formed in a LFA-1-dependent manner. Upon antigenic stimulation, the tolerized T cells could indeed activate Rap1, which is critical for LFA-1 activation and thus cell adhesion. However, orally tolerized T cells showed defects in the translocation of TCR, PKC-theta, and lipid rafts into the interface between T cells and APCs. Translocation of TCR and PKC-theta to lipid raft fractions upon antigenic stimulation was also impaired in the tolerized T cells. Ag-induced activation of Vav, Rac1, and cdc42, which are essential for immunological synapse and raft aggregation, were down-regulated in orally tolerized T cells. These results demonstrate that orally tolerized T cells can respond to specific Ags in terms of conjugate formation but not with appropriate immunological synapse formation. This may account for the hyporesponsive state of orally tolerized T cells.