Abstract
Adhesion of ETEC to the small intestinal mucosa is an essential event in colonisation and the development of diarrhoeal disease. Special classes of protein fimbriae termed Colonisation Factor Antigens (CFA) promote mucosal adhesion of ETEC. We have previously demonstrated secretory IgA (sIgA) antibody to ETEC CFA/I in human milk. In this study we tested the anti-adhesive effect of such antibody using an in vitro isolated human enterocyte adhesion assay. Bacterial adhesion was quantitatively assessed by counting the nunber of bacteria adhering to the brush border of 100 enterocytes and an adhesion index defined as the number of adherent bacteria/brush border. ETEC strain M109C2 producing CFA/I had an adhesion index of 2.2 (range 2.1-2.4) whereas the same strain lacking CFA/I had an adhesion index of 0.02 (range 0-0.03). At a dilution of 1:10, 6 human milk specimens from Sri Lankan women with demonstrable CFA/I-specific sIgA antibody produced a marked reduction in adhesion index from 2.2 to 0.16 (range 0.05-0.25) whereas 6 milk specimens with no demonstrable CFA/I-specific sIgA showed no reduction in adhesion index (mean 2.2, range 2.1-2.6). These results strongly suggest an anti-adhesive protective role for the CFA/I-specific sIgA in human milk. The presence of anti-CFA/I antibody only in milk from Sri Lankan women and not in any of 75 Caucasian, U.K. women tested presumably reflects prior exposure only of the Sri Lankan mothers to CFA/I-positive ETEC.
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