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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Differences in the Frequency of the Hinge Variants of Porcine Iga Is Breed Dependent

Authors
item Navarro, P - U IOWA, IOWA CITY IA
item Christenson, R - MEAT ANIMAL RES CENT NE
item Ekhardt, G - PIC USA FRANKLIN KY
item Lunney, Joan
item Rothschild, M - DEPT ANIM SCI AMES IOWA
item Lemke, J - DEPT PREV MED IOWA
item Butler, J - DEPT MICROBIOL IOWA

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 1999
Publication Date: N/A

Interpretive Summary: Swine use certain proteins, the immunoglobulins (Igs), in responding to infectious disease challenge and to vaccines. Certain types of Igs are localized to certain tissues. The IgAs are at mucosal surfaces, e.g., the nose, lung, intestine. At these sites the IgAs help to prevent infections from spreading. In an effort to understand the complexity of the IgAs in pigs, genetic studies of a wide range of commercial and experimental pig breeds were screened for their IgA genetic type, termed allotype. Only two types have been found in pigs, the a and b allotypes, so pigs could express thee homozygous a/a or b/b or heterozygous a/b allotypes. When analyzed with regard to breed, a very strong association between breed and the frequency of the a and b allotypes was discovered. Meishan and NIH minipigs were homozygous for IgAa. Heterozygotes animals predominated in Berkshire, Chester White, Durocs, Hampshire, Landrace and White Cross breeds while b/b homozygotes were best represented in the White Cross line This very strong breed dependency of IgA allotypy in swine resulted in a sample bias which explains why an earlier study found only two b/b homozygotes (1.3%). Those samples came from primarily Landrace and Yorkshire animals, thus, the expected frequency of b/b homozygotes would be <3%. The current data shows the expected frequency of the different IgA allotypes in pigs and rejects the earlier hypothesis that b/b animals are selected against and that a/b heterozygote are positively selected. This report does not support the view that IgAb molecules predispose animals to a higher risk of postnatal mortality. Survival data among the offspring of at least Duroc and White Cross animals offer no evidence that IgAb is any less effective in mucosal immunity.

Technical Abstract: Initial studies on the distribution of the IgAa and IgAb alleles of porcine IgA in over 160 randomly-selected animals revealed an abundance of heterozygotes but only two b/b homozygotes suggesting that this genotype may be at a disadvantage while heterozygous individuals may be at some advantage. Since the structural difference between IgAa and IgAb involves hinge length, numerous hypotheses could explain the unexpected allotype frequency differences among adult swine. We present data on 398 additional animals to show that when breed was not considered, young animals of known parentage, had genotypic frequencies identical to that expected for Mendelian alleles but that a/b heterozygotes were overrepresented in adults. When analyzed with regard to breed, a very strong association between breed and the frequency of the IgAa and IgAb alleles was discovered. Meishan and NIH minipigs were homozygous for IgA. Heterozygotes animals predominated in Berkshire, Chester White, Durocs, Hampshire, Landrace and White Cross breeds while b/b homozygotes were best represented in the White Cross line. This very strong breed dependency of IgA allotypy in swine can produce a sample bias which can explain why we found only two b/b homozygotes (1.3%) in the earlier study. Since the original samples came from primarily Landrace and Yorkshire animals, the expected frequency of b/b homozygotes would be expected to be <3%. The data presented here reject the hypothesis that b/b animals are selected against and that a/b heterozygote are positively selected.

Last Modified: 10/30/2014