T-cell control of IgA production. I. Distribution, activation conditions and culture of isotype-specific regulatory helper cells.

The capacity of T cells from different sites to augment IgA production by LPS-stimulated B cells has been investigated. Peyer's patch T lymphocytes activated with Con A induced up to a 20-fold increase in IgA production. The effect was isotype-specific, in that no consistent effect on IgG and a diminution of IgM synthesis were observed. Less activity was recorded in spleen and mesenteric lymph node T cells. Optimal activation of the Thy 1+ Lyt 1+2- helper cells required the addition of splenic adherent cells and the elimination of Thy 1+ Lyt 2+ suppressor cells prior to activation. T lymphocytes maintained regulatory activity for several months after expansion in medium supplemented with IL-2 and are now being cloned. We conclude that IgA production is under control of T cells sited preferentially, but not exclusively, in gut-associated lymphoid tissue, and that these T cells can augment IgA production by B lymphocytes from sites with low commitment to production of this isotype.