Mechanism of acquired resistance against Legionella--blastogenic responses of murine spleen lymphoid cells following the stimulation with Legionella antigens

We have tried to characterize the blastogenic responses of murine spleen lymphoid cells from BALB/c mice immunized with Legionella pneumophila serogroup (SG) 1 (Philadelphia 1 strain) and non-treated mice. Lymphoid cells from immunized mice showed stronger blastogenic responses following stimulation with concanavalin A or formalin-treated L. pneumophila SG1 whole cell antigen than those showed by lymphoid cells from non-treated mice. These cells from immunized mice also responded strongly when stimulated in vitro with other SGs of L. pneumophila, while these responded weakly when stimulated with other species of Legionella. Serum antibody titers of immunized mice against each SG of L. pneumophila were examined and the cross reactions were also recognized. However, the relatedness of serum antibody titers and the blastogenic responses against each serogroup of L. pneumophila was small. The epitopes recognized by the cellular immunity might be different in part from those recognized by serum antibodies, and investigations should be made on what the cellular immunity recognizes and how it works.