Enterotoxigenic Escherichia coli (ETEC) adhere to
the intestinal mucosa by a number of
fimbrial colonization factors (CFs) that have been claimed to induce only
type-specific
immunity. However, adult Bangladeshi patients infected with CFA/I-expressing
bacteria,
developed significant plasma IgA antibody responses, as determined by enzyme-linked
immunosorbent assay, not only against the homologous fimbriae
but also against several
heterologous CFs, i.e. CS1, CS2, CS4 and PCFO166 fimbriae. In contrast,
North American
volunteers, who had probably not been infected by ETEC previously,
responded with serum
IgA against CFA/I fimbriae but not against any other CFs after
symptomatic infection with
CFA/I-expressing ETEC. Thus, infection with CFA/I-expressing
bacteria may boost immune
responses against CFs with a related amino acid sequence in
previously primed subjects.