Mechanisms for Mucosal Immunogenicity and Adjuvancy of Escherichia coli Labile Enterotoxin

Abstract

Escherichia coli labile toxin (LT) was assessed as mucosal immunogen and as adjuvant for tetanus toxoid (TT) in mice. After oral administration of LT, C57BL/6(H-2^b) and BALB/c (H-2^d) mice were high mucosal and serum antibody responders, while C3H/HeN (H-2^k) mice were low responders. High responders exhibited mainly serum IgG (including IgGl, IgG2a, and IgG2b), as well as IgM and IgA, while mucosal responses were IgA. Analysis of LT-B-specific CD4⁺ T helper (Th) cells from Peyer's patches (PP) or from spleen revealed a mixed Thl (interferon-γ) and Th2 (interleukin4 and -5) cell pattern. Oral LT given with TT induced TT-specific response patterns identical to LT-B. Analysis of mRNA from TT-specific PP CD4⁺ Th cells also revealed a mixed Thl- and Th2-type response. Thus, antibody response profiles induced by LT are regulated by both CD4⁺ Thl and Th2 cell types.