THE V-H AND C-H IMMUNOGLOBULIN GENES OF SWINE - IMPLICATIONS FOR REPERTOIRE DEVELOPMENT

Swine have the largest number of IgG subclass genes of all species so far studied but have a single gene for IgA which occurs in two allelic forms that differ in hinge length. Swine also have constant region ge nes for C mu and C epsilon, but lack a gene homologous to that which e ncodes IgD in rodents and primates, despite the otherwise high degree of sequence similarity of all other swine C-H genes with those of huma ns. Swine have < 20 V-H genes, a single J(H) and perhaps a limited num ber of D-H segments. Newborn piglets show preferential V-H and D-H usa ge and may use gene conversion as a mechanism for expanding their anti body repertoire. Despite the close similarity of their Ig gene sequenc es to humans, swine belong to the group of animals that includes rabbi ts, chickens and cattle when classified on the basis of B cell develop ment. This group, unlike rodents and humans, have a single V-H family, use hindgut follicles early in life (rather than bone marrow througho ut life) to diversify their antibody repertoire and probably all use g ene conversion. It is proposed that IgD may serve a function in repert oire development in rodents and humans which is unnecessary in the chi cken-lagomorph-artiodactyl group. The diversity of immunoglobulins and immunoglobulin genes among species justifies the quest of veterinary immunologists to define the system for their species of interest rathe r than making extrapolations from mouse and human immune systems.