Lymphokine production by C3b-stimulated B cells.

Trypsin cleavage of guinea pig C3 (60 sec, 20 degrees C) yields a fragment which stimulates guinea pig lymphocytes to produce a chemotactic lymphokine. These digested C3 preparations possess only minimal inherent chemotactic properties. The response is completely inhibited by prior adsorption of the trypsin-derived C3 fragments with insolubilized anti-C3. The active C3 fragment is C3b as demonstrated by the elution of activity in the exclusion volume of Sephadex G-75 (m.w. greater than 50,000 dalton). The C3b-dependent cellular-derived chemotactic factor is present in the supernatants of B cell cultures and totally absent in those of T cell cultures. Generation of this lymphokine occurs in the absence of cellular proliferation.