Blastogenic responsiveness of spleen cells from guinea pigs sensitized to Legionella pneumophila antigens.

An in vitro leukocyte blastogenic assay was utilized to establish an in vitro correlate of cell-mediated immunity to Legionella pneumophila antigen with spleen cells from sensitized guinea pigs. Incubation of spleen cells from sensitized but not normal guinea pigs with graded amounts of killed whole cell Legionella bacteria or sonicate derived from the bacteria resulted in an antigen-induced blast cell proliferation as evidenced by an increased uptake of [3H]-thymidine into spleen cell cultures. Peak responses occurred approximately 4-6 days after incubation of the spleen cells with antigen. Sensitivity of spleen cells from animals immunized with Legionella vaccine in adjuvant persisted for at least 150 days, while responses after infection of guinea pigs with viable bacteria persisted about 4-6 weeks. The blastogenic responses of the spleen cells to Legionella antigen appeared to be a correlate of cell-mediated immunity.