Heterogeneity of the plasma cell response to bovine staphylococcal mastitis: an ultrastructural study

Mammary tissue samples from glands of dairy cows with chronic Staphylococcus aureus mastitis were examined by light and transmission electron microscopy. Cytological observations were limited to the mucosal tissues of the gland and teat cisternal areas where accumulations of lymphoid cells predominated. Plasma cells were the most numerous leucocyte type present in these areas and exhibited varied ultrastructural characteristics. Although the majority of plasma cells were normal in appearance, cells with abnormal ultrastructure were frequently observed, including cells with distended rough endoplasmic reticulum, cells with cytoplasm entirely engorged with immunoglobulin, and necrobiotic cells. Results demonstrated copious production of local immunoglobulins, predominantly IgG, in response to staphylococcal infection. Atypical cell types observed may have indicated a functional disturbance of immunoglobulin secretion associated with chronic mastitis.