Klebsiella pneumoniae stimulate highly purified human blood B cells to mature into plaque forming cells without prior proliferation.

The plaque forming cell (PFC) and proliferative responses of human peripheral blood lymphocytes and highly purified blood B cells induced by pokeweed mitogen (PWM) and group A streptoccocal cell membranes (A-ScM) were compared with the responses triggered by various cell preparations of Klebsiella pneumoniae K 43 (Klebs). The number of PFC was determined by a protein A plaque assay, and lymphoproliferation was measured by 3H-thymidine incorporation. In cell cultures stimulated with PWM and A-ScM, lymphocyte proliferation appeared to be associated with the generation of PFC. Klebs caused development of PFC without measurable prior proliferation. Whereas the response to PWM and A-ScM was absolutely T cell-dependent, highly purified B cells generated PFC when incubated with Klebs. Moreover, restitution of T cells to the B cell fraction did not augment (or diminish) the number of plaques. These studies establish that Klebs cell envelope structures contain a T cell-independent polyclonal B cell activator for human B lymphocytes in a high stage of differentiation. Use of this probe should provide further insight into the cellular interactions involved in the differentiation of antibody forming cells in humans.