BACTERIAL AGENTS STIMULATE THE RELEASE OF SECRETORY IGA FROM HUMAN MILK LEUKOCYTES

Abstract

Recently we reported that the secretion of secretory IgA (SIgA) from human milk leukocytes was stimulated by phagocytosis (J. Infect. Immun. 34: 498, 1981) and certain surface membrane stimuli including N-formyl-L-methionyl-L-phenylalanine (J. Immunol. In Press, 1984). Since that synthetic peptide is similar to ones secreted by certain strains of enteric bacteria, we questioned whether other bacterial products also trigger the release of that immunoglobulin from phagocytes in human milk. Supernatent fluids from cultures of Escherichia coli 07KL or Klebsiella pneumoniae obtained by passage through 0.22μ filters lead to the release of 40-50% of the SIgA found in unfractionated human colostral leukocytes (p<0.01). A similar degree and temporal pattern of SIgA release occurred when those leukocytes were exposed to heat-treated filtrates from those bacterial cultures, purified lipopolysaccharide from E. coli or type 1 pili isolated from K. pneumoniae.Thus, the secretion of SIgA by human milk leukocytes is initiated not only by phagocytosis of intact microorganisms, but also by important components of certain enteric bacterial pathogens. Furthermore, these findings support the hypothesis that SIgA released from those leukocytes plays a role in protecting the breast-fed infant from bacterial infections of the gastrointestinal tract.