Humoral and cellular factors affecting the neutrophil response of the locally immunised mammary gland to staphylococcal infection.

Locally immunising the non-lactating ovine mammary gland by infusing killed Staphylococcus aureus enhances neutrophil accumulation in mammary secretion during subsequent staphylococcal infection. Immunological factors influencing this increased neutrophil response were studied in the present experiments. Glands locally immunised with killed Brucella abortus supported a greater neutrophil response to staphylococcal infection than did glands immunised with killed S. aureus. An enhanced neutrophil response to staphylococcal infection was recorded in 3 of 7 ewes locally immunised with zymosan. Passive immunisation by intramammary infusion of secretions from immunised glands conferred an enhanced neutrophil response during staphylococcal infection. Absence of haemolytic complement in secretions of immunised glands suggested complement was not implicated in the response. Secretions of immunised glands contained elevated concentrations of mononuclear cells. When exudates rich in mononuclear cells were established by infusion of endotoxin into non-immunised glands there was no increase in the neutrophil response to subsequent staphylococcal infection. However, when the mononuclear cell concentration was elevated by intramammary infusion of staphylococcal antigens in systemically immunised ewes there was an increase in the neutrophil response to subsequent infection. Thus humoral and cellular characteristics of the locally immunised mammary gland influence the kinetics of the neutrophil influx during staphylococcal infection.