Different T cell subset stimulation by IgG1 or IgG2a anti-T3 antibodies

In so-called responder cell cultures--able to be stimulated by mouse IgG1 anti-T3 antibodies (IgG1-CD3)--the proliferation, IL 2 secretion and IL 2 receptor expression were lower in IgG1-CD3 than in IgG2a-CD3-stimulated cultures. Using a double-fluorescent technique, we found that IgG1-CD3 antibodies stimulate fewer T4 cells, but the same amount of T8 cells, than IgG2a-CD3 antibodies. The suboptimal T4 cells stimulation could be enhanced by adding exogenous IL 2 or by crosslinking the IgG1-CD3 antibodies by plastic-bound goat anti mouse IgG antibodies. Following antibody-mediated crosslinking, high IL 2 levels could also be found in IgG1-CD3-stimulated cultures. We conclude that CD3 antibodies of the mouse IgG1 isotype stimulate fewer T4 cells, due to insufficient crosslinking by monocytes and that T3 structure crosslinking is essential for optimal IL 2 production and secretion.