The Hemolytic Immunoglobulins Produced by Unirradiated and Irradiated Rabbits Immunized with Forssman Antigen

Initial hemolysin responses reached high peak titers in rabbits intensely immunized with the Forssman antigen in minced horse kidney. They reached equally high peak titers, although the latent periods were prolonged, in rabbits heavily irradiated with 500 r 2 days before the start of intense immunization. In sharp contrast, peak titers were markedly depressed as well as delayed in irradiated rabbits given only 1 injection of horse kidney. Anamnestic hemolysin responses in unirradiated rabbits or in those that had recovered from irradiation exhibited the typically faster reactivity as compared to the initial response, and a more intense anamnestic response developed when preceded by an initial protracted immunization than when preceded by a single injection of antigen. The anti-Forssman sera from these various immunization procedures were tested for their IgM and IgG immunoglobulin contents by starch block electrophoresis, sucrose gradient separation, and 2-mercaptoethanol treatment. The IgM type predominated. The IgG type formed less than 5% of the hemolytic activity during the initial hemolysin rise and decline following single or repeated injections of antigen, and it increased in amount during the anamnestic response. It sometimes increased to 10 to 15% following a single reinjection of antigen and often predominated during hyperimmunization with repeated reinjections of antigen. Hemolysin of the IgM type was more avid than that of the IgG type. Heavy total doses of irradiation 2 days before the injection of antigen suppressed the formation of both immunoglobulins.