Quantification and immunoglobulin classification of plasma cells in nonlactating bovine mammary tissue.

Plasma cell populations in bovine mammary tissue were examined during involution using electron microscopic and immunohistochemical techniques. Biopsies were taken from each quarter of five Jersey cows at weekly intervals beginning at drying off through parturition. Ultrastructural examination of stromal plasma cells revealed rough endoplasmic reticulum cisternae engorged with flocculent material, indicative of antibody synthesis. Plasma cells were observed proximal to alveolar epithelial cells. This association may facilitate transport of antibody through epithelium and into milk. Immunoglobulin-producing plasma cell numbers increased gradually from drying off, reached peak concentrations 2 wk prepartum, and dropped significantly during the last 2 wk of gestation. Plasma cells producing immunoglobulin G1 and G2 were the most numerous types observed during the nonlactating period followed by cells producing immunoglobulin M and immunoglobulin A. Plasma cells producing immunoglobulin were more numerous during the last 2 wk of gestation and in tissue infected with minor pathogens than in uninfected quarters. Exposure to minor pathogens may have enhanced sensitized B-lymphocyte proliferation into antibody producing plasma cells through antigenic stimulation. Results of plasma cell distribution during the nonlactating period in bovine mammary tissue indicate times when local immunostimulation of B-lymphocytes may be most effective in enhancing immunity to intramammary infection.