Th1 and Th2CD4(+) T cells provide help for B cell clonal expansion and antibody synthesis in a similar manner in vivo

The relative ability of Th1 and Th2 T cells to help B cells remains controv ersial as do the mechanisms by which both T cell subsets provide help in vi vo. Whether this help affects the clonal expansion and/or differentiation o f B cells has been difficult to assess due to the low frequency of Ag-speci fic T and B lymphocytes, We have employed a novel technique to directly mon itor the clonal expansion of Ag-specific T and B lymphocytes in vivo, OVA-s pecific TCR transgenic T lymphocytes were polarized toward a Th1 or Th2 phe notype in vitro, These cells were then transferred into syngeneic recipient s, along with B cell receptor transgenic hen egg lysozyme-specific B lympho cytes. Our results indicate that Th1 and Th2 cells support B cell responses to a similar extent in vivo and that they achieve this in the same manner by migrating into B cell follicles to promote CD154-dependent B cell clonal expansion and Ab production.