Submitted to: Molecular Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2000
Publication Date: 8/20/2000
Citation: Navarro, P., Christenson, R.K., Weber, P., Rothschild, M., Ekhardt, G., Butler, J.E. 2000. Porcine IgA allotypes are not equally transcribed or expressed in heterozygous swine. Molecular Immunology. 37(11):653-664. Interpretive Summary: In mammals, development of the immune system is critical to survival and normal growth and development. Immune system development in swine and other livestock species is unstudied as compared to more commonly studied humans and mice. The DNA of peripheral blood leucocytes from fetal, neonatal, and adult pigs of different breeds was transcribed and measured by molecular biology techniques (RT-PCR). Deviations from expected 1:1 ratio of allotypes transcripts in different breeds of swine can be highly significant in neonatal and adult animals but not in fetal animals. Fetuses are not exposed to environmental antigens and maternal regulatory factors because of maternal/fetal placentation. Therefore, fetuses do not deviate from expected ratios of allotypes. Characterization of development changes in pig immunity are important to the swine and veterinary industries for improving neonatal pig survival and developing of specific protective immunity systems (disease vaccination protocols) for neonatal pigs.
Technical Abstract: A prediction of 1:1 expression of constant region allotypes in different breeds of swine assumes that initial productive VDJ rearrangements are random between chromosomes, switch recombination is random, there is no allele-related defect in switching and that there is no selection for a B- cell receptor bearing a certain constant region allotype. In data reported here, this prediction is only approached for the IgAa and IgAb alleles of porcine IgA in late term fetal piglets that because of swine placentation, have no exposure to environmental antigen or maternal regulatory proteins. In the spleen, thymus, mesenteric lymph node (MLN), ileal Peyer patches, parotid gland and PBLs of five-week-old conventionally-reared Duroc pigs, ratios of IgAa to IgAb transcripts as high as 4:1 were observed. In contrast, 21 of 23 White Cross animals had higher levels of IgAb than IgAa in their PBLs (some > threefold) suggesting that an allele-linked switch defect is unlikely to explain the results. Analyses of the IgAa:IgAb ratio in Durocs of different age and reared at different sites, provided no evidence that differential transcription was breed-dependent. When serum levels of the two allotypes were measured in conventionally-reared animals, allotype expression agreed very closely with transcript levels in PBLs. We speculate that such deviations in this species could result from (a) exposure to environmental antigens that selectively expand B-cells expressing VH gene alleles linked to either IgAa or IgAb, (b) colostral auto-allotypic suppression, or (c) differential regulation of trans- switching.