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.