The effects of various preparations of guinea pig serum on the Gardner lymphosarcoma 6C3HED in C3H mice were studied. Complete regression of tumor as well as marked retardation of growth were noted as a result of treatment with the following sera: (1) normal; (2) depleted of complement 1 (R1); of complement 3 (R3), and of complement 4 (R4); (3) depleted of properdin (RP); (4) heated at 56 C. for 20 minutes and for 60 minutes and at 66 C. for 30 minutes; and (5) supernatant from centrifuged at 35,000 G at 2 C. for 3 hours. No tumor inhibitory effect was noted as a result of treatment with (1) serum depleted of complement 2 (R2) and (2) pellet (containing lipopolysaccharides) from serum centrifuged at 35,000 G at 2 C. for 3 hours. These results indicate that the tumor inhibitory principle (TIP) in guinea pig serum is probably not complement, properdin, or lipopolysaccharide.
Properdin titers of sera from mice treated with each of the preparations listed above disclosed low properdin levels when the tumors were growing or were large, and normal or elevated properdin levels when the tumors were regressing or disappeared completely. In addition, normal nontumor-bearing mice showed as much as a threefold increase in properdin levels when treated with normal or heated guinea pig serum.
While it is possible that the tumor inhibitory principle (TIP) in guinea pig serum may exert its effect through the animal’s own properdin system, such a relationship has not as yet been demonstrated.