ISOTYPE AND ANTIBODY SPECIFICITY OF SPONTANEOUSLY FORMED IMMUNOGLOBULINS IN PIG FETUSES AND GERM-FREE PIGLETS - PRODUCTION BY CD5(-) B-CELLS

Pig fetuses, colostrum-deprived newborns and germ-free (GF) piglets, a nimals in which B-cell development is not influenced by maternal regul atory factors, were employed to study the occurrence and specificity o f natural antibodies (NAb). Serum immunoglobulins of all isotypes were found in 44-day-old fetuses (the gestation period in pigs lasts 114 d ays) and their level, with predominating IgM, was increased during fet al ontogeny. In sera of fetuses at the end of embryonic life as well a s of newborns and older GF piglets, antibody activity against autoanti gens (thyroglobulin, hormones, ssDNA), phylogenetically conserved prot eins (myosin), haptens (trinitrophenyl; TNP) and bacterial components (Escherichia coli 086, tetanic anatoxin) was detected by enzyme-linked immunosorbent assay. The antigen-binding activity of IgM NAb increase d after isolation of the serum immunoglobulins on a Staphylococcus Pro tein A (SPA)-Sepharose column. IgM reactivity similar to that detected in serum was found in supernatants from polyclonally stimulated cultu res of spleen of 8- and 12-day-old GF piglets. Pig fetal liver IgM(+) B cells, which were able to produce IgM after polyclonal stimulation, did not express the CD5 molecule. Our results indicate that pig preimm une repertoire is comparable to that described in humans and mice, alt hough in contrast to these species pig B-1 cells do not express CD5.