Detection of precursor Th cells in mesenteric lymph nodes after oral immunization with protein antigen and cholera toxin

We have characterized the earliest antigen-specific Th cells in murinemesenteric lymph nodes (MLN), following oral immunization with the hen egglysozyme (HEL) as antigen and cholera toxin (CT) as adjuvant. We did thisby analyzing in vitro proliferation and cytokine production in response toHEL by the MLN T cells. MLN cells taken 5 days after a single oralimmunization with HEL and CT provided the earliest source of proliferatingHEL-specific T cells. This proliferation was completely inhibited byanti-IL-2, but not inhibited by anti-IL-4 antibody. IL-2 protein wasdetected in culture supernatants but not IL- 4 using ELISA or bioassays.IL-4 mRNA was not found in responding cells using RT-PCR. Some of the day 5MLN cultures produced IFN-gamma in response to HEL, but isolated T cellsfrom the same MLN did not. Exogenous IL-4 alone did not stimulate day 5 MLNT cells, but IL-4 did synergize with HEL to induce a large proliferativeresponse. The data indicate that the HEL-specific CD4 T cell pool in MLN 5days after oral immunization is composed of undifferentiated precursor Thcells. These cells have the potential for IL-2 production and IL-4Rexpression upon re-stimulation in vitro.