B1B 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(-/-) mi ce compared to normals while IgM(+)/CD23(+) (B2) cell numbers were reduced threefold. Intestinal antibody levels were also determined for both total i mmunoglobulin and phosphorylcholine (PC)-specific and LPS-specific antibody following oral challenge with attenuated Salmonella typhimurium. Total imm unoglobulin levels (IgM, IgG, and IgA) were reduced 60-80% in intestinal se cretions of IL6(-/-) mice compared to wild-type controls; however, PC-speci fic 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 t he development of mucosal B2 cells is impaired but that intestinal B1 cells responding to microbial antigens such as PC and LPS develop normally and a re fully functional. (C) 1999 Academic Press.