Dextran-conjugated anti-Ig antibodies as a model for T cell-independent type 2 antigen-mediated stimulation of Ig secretion in vitro. I. Lymphokine dependence.

We have previously demonstrated that dextran-conjugated anti-IgD antibodies (anti-delta-dex) stimulate high levels of B cell proliferation at concentrations that are 1000-fold lower than that required by unconjugated anti-Ig. We now show that anti-delta-dex may provide a suitable model to study Ig secretion stimulated by soluble T cell-independent type 2 Ag exemplified by TNP-Ficoll. Thus, both TNP-Ficoll and anti-delta-dex stimulate low to undetectable levels of Ig secretion when cultured with resting B cells. Addition of IL-5 or IL-2 stimulated enhanced anti-TNP responses in the presence of TNP-Ficoll, or induced polyclonal Ig secretion in the presence of anti-delta-dex. Both TNP-Ficoll and anti-delta-dex conjugates stimulated Ig production by Percoll-separated low density (partially activated) B cells in the absence of added lymphokines. These findings point to the similarities in the activation requirements of TNP-Ficoll and anti-delta-dex and suggest that dextran-anti-Ig conjugates, which can induce B cell activation irrespective of Ag specificity, may provide a useful model for studying various parameters that characterize the responses to soluble TI type 2 Ag.