C3 and colon carcinoma: It has been shown that intracellular C3 in human colon carcinoma Caco2 cells can cleave cathepsin L and B and release C3a, just like CTSL can cleave C3 in CD4+ T cells in a non-C3 convertase manner, and C3a secretion can be downregulated by treatment with cathepsin L and B inhibitors in these cells (50).