Human milk immunoglobulin A antibodies to Shigella virulence determinants

Because human milk is thought to protect infants from shigellosis, we evaluated milk for immunoglobulin A to Shigella virulence determinants. Milk was preincubated to remove antibodies unrelated to each locus of interest, using defined Shigella and E. coli hybrids containing known Shigella genetic segments prior to immunoblotting. The milk could not be shown to contain antibodies to chromosomally encoded virulence loci except for the expected antibodies to the products of the histidine locus. However, all the milk samples contained antibodies to antigens encoded by the large virulence plasmid. The finding of these antibodies suggests a possible mechanism by which human milk might protect infants.