IL-6-DEFICIENT MICE EXHIBIT NORMAL MUCOSAL IGA RESPONSES TO LOCAL IMMUNIZATIONS AND HELICOBACTER-FELIS INFECTION

Using IL-6-deficient (IL-6 -/-) or wild-type mice, we investigated whe ther IL-6 is involved in the intestinal adjuvant activity of cholera t oxin (CT) and to what extent IL-S is required for mucosal IgA response s against soluble protein Ags or live Heli-cobacter felis infection, I n naive IL-6 -/- mice we found normal total IgA levels in serum, bronc hial and intestinal lavage and unaltered frequencies of IgA plasma cel ls in intestinal lamina propria, In Peyer's patches (PP) and mesenteri c lymph nodes (MLN) IgA-producing cells were as frequent in IL-6 -/- a s in wild-type mice, Immunohistochemical analysis of PP revealed germi nal centers that co-localized IgA(+) cells, indicating B cell activati on and isotype switching in situ in the intestinal immune inductive si te, Phenotypic analysis of the distribution of conventional B-2 cells (B220(+)CD5(-)/Mac-1(-)) and B-1 cells (B220(+), CD5(+)/Mac-1(+)) in i ntestine-associated tissues gave comparable results in IL-6 -/- and wi ld-type mice, The ability to respond with mucosal IgA following oral a nd intranasal immunization with specific Ag, KLH or OVA, in the presen ce of CT adjuvant or to live H. felis infection was similar in IL-6 -/ - and wild-type mice, CT exerted strong and comparable adjuvant functi ons in IL-6 -/- and wild-type mice, Repeated oral immunizations with C T alone stimulated immune protection against CT-induced diarrhea in li gated loops that was of similar magnitude in IL-6 -/- and wild-type mi ce, We conclude that, although IL-6 has been ascribed a crucial role i n terminal differentiation of IgA B cells in vitro, we found no eviden ce to support the notion that IL-6 is critically required for IgA B ce ll development or specific mucosal IgA responses in vivo.