Mammary tumor immune enhancement in mice by local hyperemia

The mammary carcinoma MC2 causes a strong immune response in syngeneic, female C3H/He mice, and growing s.c. implants will regress spontaneously in about 20% of untreated hosts. Hyperemia is part of the local immune reaction against MC2 implants. An accelerated local hyperemic reaction at MC2 implants could be created in normal mice by the i.p. injection of blood or plasma from MC2 hosts at an early (Day 17) stage of immunization. In these mice given injections, MC2 growth was enhanced, and the incidence of spontaneous regressions was reduced. Local hyperemia caused by heat also promoted the growth of MC2 implants. In contrast, injections of blood or plasma from MC2 hosts at an advanced (Day 35) stage of immunization reduced the growth of MC2 implants and increased the incidence of their spontaneous regression. It is concluded that increased blood supply to a tumor in the absence of adequate systemic immunity favors tumor growth, and that this represents a new, additional mechanism in the immune enhancement phenomenon.