Rapid establishment of a stable IL-4/IFN-gamma production profile in the antigen-specific CD4+ T cell response to protein immunization.

Development of the antigen-specific murine T cell response to immunization with keyhole limpet hemocyanin (KLH) in adjuvant has been monitored with direct limiting dilution analysis of CD4+ cells in draining lymph nodes (LN) and measurement of the cytokines produced by their clonal progeny. In vivo, the response to immunization suggested a major role for IL-4 and a minor role for IFN-gamma since IL-4 mRNA levels increased and IFN-gamma mRNA levels declined in LN over the first 3 days, and KLH-specific serum antibodies were mainly of IgG1 class with lower levels of IgE and IgG2a. Antigen-specific clonogenic cells were first detected in LN at day 4, at which time they comprised approximately 8% of the total CD4+ LN cell pool, declining to 1-2% from day 7 until at least 6 weeks after immunization. These clonogenic cells expressed high levels of surface CD44 (Pgp-1) both early and late in the in vivo response. Over the whole of the time span from day 4 to 6 weeks after immunization, most antigen-specific cells gave rise to clones that secreted IL-4 and a smaller proportion gave rise to IFN-gamma-secreting clones. By contrast, polyclonally activated CD4+ cells from untreated mice preferentially gave rise to clones with the converse cytokine profile. We conclude that a stable ratio of antigen-specific CD4+ cells committed to IL-4 or IFN-gamma synthesis is established within the first 4 days after KLH immunization and, contrary to prediction, does not evolve towards a more restricted cytokine profile during the primary response.