The induction and migration of antigen-specific helper cells for IgA responses in the intestine

The distribution of keyhole limpet haemocyanin (KLH)-specific helper cells for antibody responses of IgA, IgM and IgG isotypes in Peyer's patch (PP), mesenteric lymph node (MLN) and peripheral lymph node (PLN) was examined following oral, intraduodenal (ID), intraperitoneal (IP), intra-Peyer's patch (IPP) or subcutaneous (SC) immunization with KLH. Oral or ID immunization gave little or no response in any tissue studied. IP immunization with or without a subsequent ID challenge gave rise to a modest IgA and IgM helper response in MLN but a small IgA and IgM helper response in PP and PLN. IP immunization alone did not stimulate IgG-specific help in any tissues studied, but a small IgG helper response occurred in MLN and PLN after subsequent ID challenge. IPP was the most effective route of immunization, giving rise to a large helper response for IgA, IgM and IgG isotypes in PP, a smaller response in MLN and no response in PLN. The helper response following IPP immunization was not augmented by subsequent ID challenge. SC immunization gave a small but significant helper response for all isotypes in PLN but no response in PP or MLN. The kinetics of the helper response were examined in PP, MLN, PLN and thoracic duct lymph (TDL) following IPP immunization. The helper response for all isotypes in PP was maximal at 2 weeks and then declined. Similar kinetics but of lower magnitude were observed in MLN and TDL. The presence of IgA-specific helper cells in TDL demonstrates that these cells migrate, presumably from GALT, and may constitute an important component of mucosal responses at extraintestinal sites.