S E R U M Levels of Second C O M P O N E N T of C O M P L E M E N T in Cancer P a T I E N T S 1

Awareness that advancing cancer is often accompanied by defective imnmnologic responses, and accumulating evidence that immune reactions may influenee the course of cancer, has stimulated the study of various meehanisms of immunologic reaction in patients with cancer. As part of such a program we have determined the serum level of the second component of complement in a group of cancer patients. In a previous study, total sermn complement (C') tilers in a group of cancer patients had the same mean value as in healthy controls, although the range was broader (1). However, the hemolytic phenomenon by which complement is assayed is a complex process involving many serum constituents (2-4). Therefore, the "total complement t i ler" is generally determined by that component which is present in the lowest effective concentration, and deviations in the concentration of complement components may occur which are not detected by the usual assay for total activity. More important, the participation of the various complement components may not be identical for all immunologic reactions. For example, Nelson (3) reports that of nine components of complement which are required for sheep cell hemolysis, only four are required for specific immune phagoeytosis. Thus the level of each of the components of the complement system becomes of interest. Depressed levels of the second component of complement (C'2) have been found in patients with systemic lupus erythematosus (5) and hereditary sngioneurotie edema (6). A drop in C'2 has also been found to be an early and sensitive indicator of the homograft rejection reaction in patients bearing homotransplanted kidneys (7). Since these immunologic situations may possibly have a counterpart in defense reactions against autochthonous cancer, the present study of C'2 levels in eaneer patients was undertaken.