B1 B cell numbers and antibodies against phosphorylcholine and LPS are increased in IL-6 gene knockout mice.

Peritoneal cavity cells were isolated from IL6-gene knockout (IL6(-/-)) and wild-type mice and stained for expression of IgM, CD5, and CD23. B1 cell (IgM(+)/CD23(-), CD5(+)/IgM(+)) numbers were increased twofold in IL6(-/-) mice compared to normals while IgM(+)/CD23(+) (B2) cell numbers were reduced threefold. Intestinal antibody levels were also determined for both total immunoglobulin and phosphorylcholine (PC)-specific and LPS-specific antibody following oral challenge with attenuated Salmonella typhimurium. Total immunoglobulin levels (IgM, IgG, and IgA) were reduced 60-80% in intestinal secretions of IL6(-/-) mice compared to wild-type controls; however, PC-specific antibody was significantly higher in IL6(-/-) mice. Anti-LPS antibodies were also three- to sevenfold higher in IL6(-/-) mice compared to controls following Salmonella challenge. These data suggest that in IL6(-/-) mice the development of mucosal B2 cells is impaired but that intestinal B1 cells responding to microbial antigens such as PC and LPS develop normally and are fully functional. Copyright 1999 Academic Press.