PERIPHERAL IMMUNE TOLERANCE BLOCKS CLONAL EXPANSION BUT FAILS TO PREVENT THE DIFFERENTIATION OF TH1 CELLS

Clonal energy in Ag-specific CD4(+) T cells is shown in these experime nts to inhibit IL-2 production and clonal expansion in vivo. We also d emonstrate that the defect in IL-2 gene inducibility can be achieved i n both naive and Th1-like memory T cells when repeatedly exposed to aq ueous peptide Ag. Nevertheless, this induction of clonal energy did no t interfere with the capacity of naive T cells to differentiate into T h1-like effector cells, nor did it prevent such helper cells from part icipating in T-dependent IgG2a anti-hapten responses and delayed-type hypersensitivity reactions. Thus, clonal energy can contribute to the development of Ag-specific immune tolerance by limiting the size of a Th cell population, but not by disrupting its effector function.