Polyclonal activation of murine B cells by a membrane proteoglycan of Klebsiella pneumoniae.

The lymphocyte activating properties of a membrane proteoglycan (MPG) extracted from a mutant non-encapsulated strain of Klebsiella pneumoniae (Kp) (biotype a I-145) were investigated. Kp MPG induced a strong proliferative response of BALB/c spleen cells and Peyer's patches cells. Thymidine incorporation was dose-related (from 1 to 100 micrograms Kp MPG/ml) and reached a maximum at day 3. It was not reduced by removal of most adherent cells, nor by depletion of Thy1-2 positive cells, but it was abrogated by removal of surface immunoglobulin bearing cells. Spleen cells from nude mice and those from C3H/Hej mice were strongly stimulated by Kp MPG. Conversely Kp MPG did not induce interleukin 2 production and did not trigger the proliferation of thymocytes but stimulated interleukin 1 production by adherent spleen cells. Finally, unfractionated or B-enriched spleen cells cultured with Kp MPG synthesized IgM and, to a lesser extent, IgG and IgA. It is concluded that Kp MPG is a T-independent polyclonal B cell activator and an inducer of interleukin 1 production.