Figure 1.

Schematic view of type 3 immunity governing neutrophilic inflammation in the infected mammary gland. A The healthy MG is an immunologically quiet place at homeostasis as there is little or no bacterial stimulation. B According to the innate immunity scenario, macrophages (MΦ) or epithelial cells responding to invading bacteria attract and stimulate ILC3 that respond by secreting IL-17A. In turn, epithelial cells recruit neutrophils through chemokine secretion. C In the adaptive immunity scenario, the capture of bacteria and presentation of antigen by an antigen-presenting cell (APC) to a tissue resident Th17 cell triggers the release of IL-17A that prompts epithelial cells to secrete chemokines (including CXCL8). These chemokines recruit neutrophils that cross the epithelium to reach invading bacteria.