Legionella pneumophila-Induced Immunostimulation and Blastogenesis of Normal Mouse Spleen Cells in Vitro

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Abstract
Cell-free sonic extracts prepared from L. pneumophila serogroup 1 enhanced the uptake of [3H]thymidine by normal mouse spleen cell cultures in vitro, and stimulated an enhanced antibody response to sheep erythrocytes in immunized and nonimmunized cultures. Increased background antibody responses to other erythrocyte species also occurred, indicating that the Legionella antigen was a polyclonal B cell activator. A purified cell wall component with physicochemical properties relatively similar to endotoxin, but without toxicity for mice, had mitogenic activity for normal mouse spleen cells and immunostimulatory properties for anti-erythrocyte antibody response. Heating the sonicate or the purified somatic antigen for 10 min diminished immunoenhancing activity but had little effect on mitogenic properties. These results point to the complex effects of Legionella-derived antigens on normal lymphoid cell function and indicate that antigens derived from Legionella have marked immunomodulatory properties.