Expression of immunoglobulin G(1) receptors by bovine mammary epithelial cells and mammary leukocytes

The objective of this study was to identify and evaluate expression of IgG(1) receptors by different cell. types in mammary tissue sections and digest-dispersed cells from the bovine mammary gland. An immunohistochemical system utilizing avidin-biotin-peroxidase complex demonstrated epithelial expression of IgG(1) receptors in mammary tissue sections from cows producing colostrum but not from cows in lactation. Fluorescence flow cytometry demonstrated that cells dispersed in digests from both tissues producing colostrum and lactating tissues selectively bound IgG(1). Fluorescence flow cytometry, using monoclonal antibodies to cell surface molecules, cytokeratin, and IgG(1), revealed that leukocytes constituted the largest percentage of cells and were the predominant cell type binding IgG(1) in mammary tissue digests. Although IgG(1) binding to epithelial cells predominated in the gland during colostrum production in situ, digestion and filtration to produce single cell suspensions resulted in the loss of large numbers of epithelial cells. Studies of Ig binding of cells produced by enzymatic digestion must account for the types of cells surviving the digestion process.