Neutralization of cholera toxin by rat bile secretory IgA antibodies.

IgA-antibody (AB) activities have been elicited in rat bile against several antigens such as bacteria, erythrocytes, tumour cells, haptens and proteins (Lemaître-Coelho, Jackson & Vaerman, 1978; Hall et al., 1979; Montgomery, Lemaître-Coelho & Vaerman, 1980; Peppard et al., 1982). However, their biological significance, except for plasma clearance of immune complexes (Peppard et al., 1982) and bacterial agglutination, remains conjectural, despite their possible major contribution to rat intestinal immunity. The importance of local intestinal immunity in protection against cholera is today widely admitted (Jertborn, Svennerholm & Holmgren, 1984). Intraintestinally given cholera toxin (CT) is a potent immunogen in rats whose intestinal mucosa then harbours numerous anti-CT IgA plasma cells (Pierce, 1978). Since bile IgA in rats is largely, but not entirely, derived from intestinal synthesis (Vaerman, Lemaître-Coelho & Jackson, 1978; Manning et al., 1984), rats intestinally immunized with CT could display high levels of anti-CT IgA AB in their bile, and these AB might neutralize CT in the biologically relevant intestinal loop assay (Lange & Holmgren, 1978).