Effects of Staphylococcus Aureus infection on bovine mammary gland plasma cell populations and immunoglobulin concentrations in milk

Mammary tissues, and milk samples from 10 Staphylococcus aureus infected and 5 uninfected quarters were examined to determine numbers of immunoglobulin (Ig)- producing plasma cells in tissue and Ig concentrations in milk. Results of peroxidase-anti-peroxidase staining of tissues showed no significant differences in numbers of plasma cells between infected and uninfected quarters with the exception of increased numbers of IgG₁-producing cells at Furstenberg’s rosette. Numbers of plasma cells were highest at Furstenberg's rosette followed by parenchymal and streak canal tissue. In parenchymal tissue from uninfected quarters, IgA-producing plasma cells were observed most frequently, whereas IgG₁-producing cells were more numerous in tissue from Staph. aureus infected quarters. No significant differences in concentrations of Ig isotypes in milk from Staph. aureus infected and uninfected quarters were observed. However, concentration of Ig isotypes tended to be higher in milk from infected quarters. Immunoglobulin G₁ was highest in concentration in all quarters followed by IgA. High relative indices of occurrence of milk IgA, IgM, And IgG₁ were noted in milk from all quarters. A low index of IgG₂ in all quarters suggests that IgG₂ was nonselectively transferred from serum. Data suggests that the antigenic effect of Staph. aureus infection on the humoral immune response of the bovine mammary gland is minimal. Persistency of Staph. aureus infection may result, in part, from suboptimal stimulation of the immune system.