Defining anatomical localisation and subsets of the murine mononuclear phagocyte system using integrin alpha X (ITGAX/CD11c) and colony stimulating factor 1 receptor (CSF1-R/CD115) expression fails to discriminate macrophages from dendritic cells

The murine mononuclear phagocyte (MNP) system is a diverse population of cells, including both dendritic cells (DC) and macrophages. Expression of the integrin alpha X (ITGAX/CD11c) is commonly used to identify classical DC, and similarly expression of colony stimulating factor 1 receptor (CSF1-R/CD115) to identify macrophages. We have characterised the expression of both of these markers using a variety of transgenic mouse models. We confirmed previous observations of CD11c expression in anatomically defined subsets of MNPs in secondary lymphoid organs, including all MNPs identified within lymphoid germinal centres and mucosal intraepithelial region. The majority of MNPs in the intestinal lamina propria and lung express CD11c, and all expressed the CD115-eGFP (MacGreen) transgene. All CD11c expressing cells express CD115-eGFP regardless of location, suggesting CSF1-dependent haematopoietic derivation. To confirm this we have undertaken bone marrow adoptive transfer experiments using precursors sorted via CD115-eGFP expression and presence or lack of Gr-1 immunoreactivity. Our data reveal that CD11c expression alone does not define classical dendritic cells. These results suggest more cautious interpretation of CD11c-dependent experimentation and direct equation with uniquely DC-mediated activities, particularly in the functioning of non-lymphoid MNPs within the intestinal lamina propria.