CTLA-4 Differentially Regulates T Cell Responses to Endogenous Tissue Protein Versus Exogenous Immunogen

CTLA-4 is critical to the regulation of CD4 T cell homeostasis in vivo. However, whether CTLA-4 regulates responses to both self and foreign proteins is not clear. We have directly compared the role of CTLA-4 in controlling T cell responses to the same protein presented as an endogenous tissue Ag vs a foreign immunizing Ag. We show that CTLA-4 only modestly reduces responses to Ag administered with adjuvant, but dramatically inhibits responses to the same Ag expressed transgenically as a tissue self protein. The critical consequence of CTLA-4 engagement is to inhibit T cell accumulation in the local lymph node draining the Ag-bearing tissue, and failure of this control leads to the onset of autoimmune tissue destruction. Thus, CTLA-4 may preferentially dampen pathologic immune responses to self proteins while permitting protective immunity to foreign agents.