MRC1 and neoplasm: Further, when THP-1 monocytes were evaluated for tumor cell- or fibroblast-derived material (indicated by PKH signal), tumor cell-derived PKH26 and fibroblast derived PKH67 were found at similar levels within THP-1 cells expressing CD206 and CD163, suggesting tumor cells and fibroblasts educate monocytes to differentiate and polarize towards an M2 phenotype (Figure 6E).