Thymus Dependence of Reaginic Antibody Formation in Mice

Formation of reaginic antibodies in mice has been demonstrated by numerous investigators (1–4). These antibodies were shown to be fixed to homologous skin, being retained there for several days. They were also shown to be heat and mercaptoethanol sensitive. Thus in many of their biologic activities mouse reaginic antibodies resemble human IgE antibodies (5). Availability of genetically thymusless nude mice provided an opportunity to examine the dependence of mouse reaginic antibody formation on the presence of thymus cells. Nude mice (nu/nu) were shown to respond poorly to sheep erythrocytes in respect to formation of IgM and IgG antibodies (6–8). The immune response to sheep erythrocytes was at least partially restored by normal thymus grafts or by injection of normal thymus cells (9). Nude mice (nu/nu) and heterozygous (nu/-) derived from back-crosses to the BALB/c strain (3 to 5 generations) were obtained from Bomholtgaard, Ltd., Ry. Denmark. BALB/c mice (+/+) originated from Jackson Laboratories, Bar Harbor, Maine. All experimental animals were 10 to 12 weeks old, except for the thymus donors, who were 5 weeks old. The reconstituted nude mice received 5 107 BALB/c thymocytes injected i.v. at the time of antigen and pertussis administration. Three proteins were employed as test antigens. Egg albumin (5 times crystallized) and bovine serum albumin (1× cryst.) were provided by Fluka, AG, Buchs, Switzerland. Human γ-globulin (Fr. II) was purchased from Miles Laboratories. Kankakee, Ill. Mice were injected i.p. with a single dose of 100 µg of the test antigen mixed together with 2 × 109-killed cells of Bordetella pertussis vaccine (Swiss Serum and Vaccine Institute, Bern). Ten days later the immunized mice were bled, the blood was allowed to clot and the serum was separated by centrifugation. Each group of mice consisted of five animals. PCA activity of the sera was determined with nude mice as recipients.