Relationship between the C5 peptides chemotactic for leukocytes and tumor cells

A reciprocal relationship has been demonstrated between the generation of the leukotactic and the tumor cell chemotactic peptides from C5. Trypsin-produced C5 leukotactic peptides can be converted into tumor cell chemotactic factors by treatment with tumor cell extracts or by incubation with the alpha-globulin chemotactic factor inactivator (CFI) isolated from human serum. A similar CFI isolated from rat serum can, like the alpha-globulin CFI from human serum, generate the tumor cell chemotactic factor from the whole human serum. These results suggest that the tumor cell chemotactic factor derives from the same portion of the C5 molecule as the leukotactic peptide. Furthermore, it appears that the critical change may be cleavage of the amino-terminal portion of the leukotactic peptide. In addition, it has been shown that most normal tissues contain an enzyme-like material that is able to generate in normal human serum a factor chemotactic for tumor cells. The implications of these findings are discussed.