A naturally occurring polyclonal B cell activator of normal and autoantibody responses

Previous studies from this laboratory have demonstrated the presence of a suppressor molecule in B/W spleen cultures. Now we present evidence suggesting the existence of a polyclonal B cell activator (sPBA) spontaneously released by B/W splenocytes. Large sPBA (120,000 to 160,000 daltons) was separable from splenic inhibitory factor(s) (less than 10,000 daltons) by ultrafiltration. Reconstitution experiments demonstrated these two molecules had antagonistic effects on splenocyte mitotic events. sPBA is directly mitogenic for T cell-depleted, B cell-enriched cultures. Furthermore, sPBA augments antibody responses in the presence of antigen, or stimulates antibody responses in the absence of antigen. sPBA appears to stimulate IgG as well as IgM antibody production. sPBA stimulates significant in vivo anti-ssDNA responses in preautoimmune B/W but not DBA mice. Physiochemical studies suggest sPBA is a DNA protein complex. sPBA activity is completely lost by heating to 56 degrees C for 30 min. sPBA activity is precipitated at pH 7.8 to 8.0. Furthermore, sPBA preparations do not display significant endotoxin levels or IL 1 and IL 2 activity.