Pattern Recognition Receptors and Differentiation Antigens Define Murine Myeloid Cell Heterogeneity Ex Vivo

Recruitment of myeloid cells during inflammatory reactions plays an important role in the propagation and resolution of inflammation. However, the identification and characterization of these cells in mice has been hampered by cellular heterogeneity at the functional and phenotypic level. We have defined criteria for the rapid flow-cytometric identification of monocytes (M(o)), macrophages (MPhi), neutrophils (N(eu)) and eosinophils (E(os)) in murine tissues using novel and established myeloid markers. These criteria were applied to the study of naive mice and mice with experimentally induced inflammation, both local and systemic, and also to a murine model of tumor progression. We show that the murine 7/4 antigen and the beta-glucan receptor, Dectin-1, are particularly useful for the sub-division of myeloid cells into individual populations, even when inflammatory conditions modulate their surface expression. Furthermore, 7/4 expression allows distinction between M(o) recently recruited to a site and the resident cells already present. These studies highlight the heterogeneity of the murine M(o)/MPhi-lineage, define an extended phenotype for murine myeloid cells and greatly facilitate the ex vivo characterization of these cells during very different models of inflammation.