Dr. Kassai Tibor szerk.: Parasitologia Hungarica 1. (Budapest, 1968)

ficieiit. It is produced by immunizing another animal species with lymphocytes or thymocytes (heterologous ALS). The active serum contains precipitating and cytotoxic antiboides which agglutinate lymphocytes. The factor responsible for the suppression of the immune reaction is carried by the IgG- fraction of the serum. Its immunosuppressive effect presumably occurs, by some hitherto unexplained mechanism, through inactivation of immunologically active lymphocytes. In the treated animal, ALS frequently causes a considerable decrease in the number of lymphocytes, an effect however, not directly connected with its immunosuppressive activity. In the elimination of the immune reaction against grafted tissues or organs, treatment with ALS is highly effective. With these facts in mind the authors investigated whether the immune response of the host animal against the parasite might also be inhibited by the application of ALS. The heterologous anti-mouse ALS used in the experiment was produced by the twofold immunization of rabbits with mouse thymocytes. A check of the immunosuppressive effect of ALS was made with a skin transplantation model. The rejection period of allogenic mouse skin grafts was prolonged to 28 days due to ALS treatment, whereas the skin grafts survived for merely 11 days in the control group. The authors investigated the effects of ALS treatment on the immune response of mice infected once or twice with N. brasi liensis . ALS treatment (0.3-0.4 ml.s.c.) began 2 days before infection, and was repeated once 5 days later or every 5 days, to a total of five times. Similarly infected control groups received identical doses of normal rabbit serum, or no serum at all. The immunosuppressive effects of ALS against a primary infection by 600 larvae and a.challenge by 300 larvae on the nineteenth day were' evaluated in the basis of feacal egg counts on the sixteenth and nineteenth days and an assessment of the parasite population. Of the first infection, 193 i 93 parasites developed per host. This number had greatly reduced by the sixteenth day in the control groups, but failed to decrease in half of the mice treated with ALS.