The presence of HLA-DR antigens on lactating human breast epithelium and milk fat globule membranes.

HLA-DR antigens have been demonstrated on the secretory epithelia of lactating breast using rabbit anti-p28,33 ('Ia-like') and mouse monoclonal anti-HLA-DR 'framework'. Normal non-lactating breast, benign or malignant tumours, epithelial cells from normal breast or isolated from milk and a presumptive breast carcinoma cell line (MCF-7) were all HLA-DR-negative. HLA-DR, HLA (ABC 'framework') and beta 2-microglobulin determinants were also demonstrated on the surface of milk fat globules (MFG) which were unreactive with monoclonal antibodies to thymus cells or leucocytes. A monoclonal antibody detecting allelic HLA-DR determinants (HLA-DRw 1,2,6) was positive on 40% of MFG samples tested, positive reactions being concordant, when tested, with blood B lymphocytes. Antisera raised against MFG membranes also contain anti-HLA-DR activity. Whether the breast epithelial cells synthesize HLA-DR molecules or acquire these passively from mononuclear cells which infiltrate during lactation is not yet resolved.