Identification of a secretory IgA receptor on breast-milk macrophages: Evidence for specific activation via these receptors

Abstract

Binding of secretory IgA (slgA) to human milk macrophages was identified by rosette formation with slgA-sensitized indicator cells and competitive inhibition binding studies with [125I]-sIgA. Macrophages formed rosettes with slgA-sensitized sheep red blood cells that were inhibited by slgA (87%) but not IgG. Both IgA, and IgA2 inhibited slgA-sensitized sheep red blood cell rosette formation. Rosette formation was completely inhibited by galactose, partially inhibited by asialofetuin, and unaffected by mannose. [125I]-labeled slgA binding to macrophages reached a plateau after 60 min, was dependent on the number of macrophages in culture, and was specifically inhibited by unlabeled slgA. Incubation of macrophage monolayers with increasing concentrations of slgA-anti-IgA immune complexes resulted in a progressive increase in the oxidative burst and increased secretion of prostaglandins. These studies indicate that human milk macrophages have a receptor for slgA and that activation of these macrophages may occur via these receptors. © 1991 International Pediatric Research Foundation, Inc.