Effects of Radiation on the Initial and Anamnestic IgM Hemolysin Responses in Rabbits; Antigen Injection After X-Rays

The effects of a wide range of x-rays from 25 to 700 r on the initial and anamnestic IgM hemolysin responses were ascertained in groups of rabbits by giving an intravenous initial injection or reinjection of 108.3 fresh sheep red blood cells (SRBC)/kg rabbit from 4 hr to 2 months (and in some cases 6 months) after irradiation. Sera from the rabbits were titrated by the delicate 50% hemolysis endpoint and graphs of the responses were analyzed with respect to five parameters: length of the latent period, peak titer, length and rate of rise to peak titer and decline from peak titer. The following statistically significant modifications were revealed, as compared to corresponding initial and anamnestic responses in unirradiated control groups. 1) On the one hand, in the initial response, small doses of 25 and 100 r stimulated a) the prolonged production of hemolysin when SRBC were injected from 4 hr to a week thereafter and b) a transient high peak titer when SRBC were injected at 1 month after irradiation. On the other hand, 25 and 100 r did not stimulate the anamnestic response at all, but depressed peak titers when SRBC were given from 7 to 30 days thereafter. 2) 25 and 100 r did not modify the length of the latent period in either response. 3) Large doses of 500 and 700 r equally and intensively depressed both responses when SRBC were given from 4 hr to 2 days thereafter. Such responses were characterized by prolonged latent periods and prolonged hemolysin rises at low rates of rise to depressed peak titers. 4) Recovery from the depressing effects of 500 and 700 r began when SRBC were given 7 days after irradiation, but was more delayed in the anamnestic response than in the initial response. The foregoing differences between the initial and anamnestic hemolysin responses in rabbits, stimulated with relatively small amounts of Forssman antigen after irradiation, suggest that the immunologically competent initial cells, as compared to the activated memory cells, are more easily stimulated and less sensitive to injury, and that both types of cells are modified to a greater extent during induction than during later stages of proliferation and synthesis.