Mast Cells Are a Marked Source for Complement C3 Products That Associate with Increased CD11b-Positive Cells in Keratinocyte Skin Carcinomas.

By using immunohistochemistry and antibodies that identify complement C3c (in C3 and C3b) or CD11b receptor, we report that the proportion C3c+ mast cells and the number of CD11b+ cells are increased in basal cell carcinoma (BCC). Instead, only CD11b+ cells are increased in squamous cell carcinoma/Bowen's disease, and only slightly so in actinic keratosis. Only C3c+ mast cells are increased in psoriasis. Furthermore, C3c+ mast cells correlated positively with CD11b+ cells, and iC3b immunoreactivity was detected around tryptase+ mast cells. Therefore, mast cells may convey immunoregulatory signals through C3, C3b, and iC3b to CD11b+ cells, especially in BCC.