MHC class II⁺ macrophages preferentially infiltrate unedited regressors. (A) Representative images of tumor sections from RAG2^−/− or RAG2^−/−x γc^−/− hosts stained for MHC class II. (B) Quantification of MHC class II⁺ events and CD68⁺ events in tumor sections is shown. (C–E) Regressor and progressor cell lines were transplanted into RAG2^−/− mice and analyzed for activated MHC class II⁺ macrophages. (C) Representative FACS plots of three regressor and three progressor tumors are shown. Cells were gated on a CD45⁺PI⁻ population. (D) Percentages of activated monocyte-lineage (F4/80⁺) cell populations are shown for regressor and progressor tumor masses. Each symbol represents a different tumor cell line transplanted into 1–3 RAG2^−/− mice. (E) Frozen tumor sections of progressor and regressor tumor masses growing in RAG2^−/− mice were stained for MHC class II. Nuclei were counterstained with hematoxylin. Bar, 100 μm. **, P < 0.01. Error bars are represented by ± SEM. IHC results were reproduced at least once.