Recruitment of neutrophils by an encapsulated coagulase-negative strain of Staphylococcus simulans in the mammary gland of the mouse.

Abstract

The encapsulated coagulase-negative strain of Staphylococcus simulans (strain 76) was inoculated into the mammary glands of lactating mice. In contrast to the coagulase-positive encapsulated Staphylococcus aureus (strain M), which elicited a neutrophil response within 18 hr, strain 76 organisms multiplied in the glands but failed to elicit a neutrophil response for 3 days; they were then eliminated from the gland by 8 days. When strain 76 was inoculated into mice whose offspring had been removed 3 days earlier, a neutrophil response was induced within 18 hr and, although phagocytic ingestion was resisted for at least 42 hr, the organisms were eliminated from most glands within 5 days. Inoculation of a naturally occurring double-stranded RNA (BRL 5907) into the mammary gland induced a macrophage infiltration of the alveolar lumen that was qualitatively similar to 3 days involution. Intramammary inoculation of strain 76 18 hr after BRL 5907 resulted in a neutrophil infiltration within 6 hr. In vitro, strain 76 stimulated the release of chemotactic factors for neutrophils from bovine mammary gland macrophages. The results suggest that the recruitment of neutrophils by strain 76 in the mammary gland of the mouse is mediated by macrophages.