The Ontogeny of Mouse Salivary Gland Macrophages Is Distinct between Sexes.

Sexual dimorphism is found in gene expression and polarization of macrophages in mammals but remains unclear in the ontogeny of tissue-resident macrophages. Remarkable sex differences are present in salivary glands and risks for a related autoimmune disease, Sjögren'sdisease. Macrophages are the most abundant immune cells in healthy mouse salivary glands and essential for the maintenance of immune quiescence and tissue repair after radiation or inflammatory damages. Therefore, we compared the origins of macrophages in salivary glands between male and female mice using conditional Cx3cr1 and Ccr2 lineage-tracing approaches. We found that among salivary gland macrophages in adult mice, most are locally maintained and derived from yolk sac progenitors or perinatal monocytes in males, but much more are short-lived and continuously replenished by monocytes in females. In wild type C57BL/6 mice, female adult submandibular glands (SMGs) consistently contain more leukocytes, including classical monocytes expressing Ccr2, Ly6c, or Csf2rb and macrophages carrying these monocyte markers, as compared with male SMGs. Single-cell RNA sequencing and flow cytometry indicated that female SMG macrophages are more polarized and express several proinflammatory genes at higher levels. Meanwhile, female SMGs contain more innate lymphoid cells and T/NKT cells expressing Csf2 and other proinflammatory cytokines. The potential contributions of these sexual differences warrant further studies as they relate to Sjögren's disease, the most female-dominant autoimmune disease, characterized by chronic inflammation in salivary and lacrimal glands. Also, these differences need be considered in developing macrophage-targeting therapies of dry mouth caused by autoimmunity or radiation.