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The effect of antibodies in the intestinal tract was studied in germ-free baby pigs whoso intestinal barrier was closed to macromolecules by the peroral administration of modified cow's milk for the first 72 hours after birth. They were then all contaminated with the pathogenic strain Escherichia cell 055 in amounts of 10' bacterial cells pcr animal. The controls, which were not given any antibodies, all died within 24 hours. All the experimental animals given 12.5--50 ml immune colostrum or serum survived, while of those given 50 ml normal serum or colostrum containing natural antibodies reacting with the Escherichia cell test strain, 50~ survived. ~'o circulating antibodies were found in the serum of the experimental animals after the administration of ~rum or colostrum. The antibodies present in colostrum thus appear to protect the newborn organism directly in the intestinal tract, which is the first site of bacterial invasion, as well as after infiltration into the blood stream.

Fundamental hematological and immunological data were obtained on sexually mature germfree miniature pigs fed, after the milk diet period, with cereal-type diet sterilized by gamma-radiation, and were compared with data of control conventional animals. Germfree adult pigs had a lower count of peripheral blood leukocytes with a lower percentage of neutrophil granulocytes and without any younger forms, a lower total serum protein level with a negligible amount of gamma and alpha 2 globulin fractions and a higher serum albumin and beta globulin level. In the mesenteric lymph nodes and in spleen, surface IgA-bearing cells predominated over surface IgG-bearing cells. Also a large amount of IgA-containing cells was found in the intestinal lamina propria, where the IgG cells were present in a negligible amount. IgM cells were the most frequent surface isotype in peripheral blood. The count of blood T lymphocytes was more than doubled.

Due to its close physiological and morphological resemblance to man, the pig occupies an important position in biomedical research. The minipig lends itself particularly well to germfree research. It is easy to deliver, maintain, and utilize in isolators. The colostrum-free, newborn germfree piglet lacking passively obtained antibodies is of an exclusive use if distinguishing the factors of natural and adaptive immunity is needed. It fits also well in studies investigating the earliest mechanisms of antibody synthesis. Under germfree conditions, the pig has been proved an excellent model for testing the action of ionizing radiation as well as of selected bacterial strains when monoassociated. Recently, conventional pigs have been used also for studies in total or selective decontamination of the intestinal tract by antibiotics and strict isolation.

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14-d-old conventional piglets were picked from normal piggery, washed with disinfectants, placed into isolators suitable for germfree work, fed a sterile diet and treated with peroral antibiotics (nalidixic acid, kanamycin, and nystatin). Beginning with day 5 or 7, Enterobacteriaceae were not found in feces. The absence of these bacteria was proved by inoculation of germfree newborn piglets with caecal content. In selectively decontaminated piglets, the white blood cell count in blood had fallen to 6 X 10(9)/L; this decrease was due to an extremely low number of granulocytes (to 0.8 X 10(9)/L). On day 35, IgG-positive cells almost disappeared from the spleen, whereas IgA cells were found in an unusually great amount. Corresponding changes in serum levels were established. The colonization resistance effect in Enterobacteriaceae-deprived piglets was confirmed; settling of introduced various E. coli strains did not occur or was delayed.

An analysis of the immtmoglobulin region of porcine blood serum proved the presence of a number of protein fractions which is higher than in other animal species. The presence of antibody activity to tetanus anatoxin examined by radioimmunoelectrophoresis was found in three ~ G-globulin fractions, which could be distinguished from each other, and also in two additional fractions. One of the latter was the y-macroglobulin fraction and the other one might correspond to y A-globulin even though its mobility was higher than the mobility of ~ A-globulin of human serum. A comparison of the immunoglobulin spectrum of porcine serum, colostrum, and of the suckling pig serum after ingestion of the eolostrum showed that the main component of porcine colostrum constitutes the ~ G-immunoglobulin, even though the colostrum seems to contain other components of the latter which have a higher electrophoretic mobility. The antibody activity of colostrum was found only in fractions y G and y M. The fraction of colostrum which might correspond to ~ A did not display any activity at all. The activity in suckling pig serum was also concentrated in fractions y G and ~ M.