The immunoglobulins and immunoglobulin genes of swine.

The historical works describing the characterization of swine immunoglobulins are reviewed. The three major isotypes, IgM, IgA and IgG, have been recognized for 25 years and their concentrations in various body fluids, the location of the plasma cells throughout the body which synthesize them and their transport into lacteal secretions and absorption by the gut of the newborn piglet, have been studied by many investigators. Swine like humans, have both kappa and lambda light chains and their frequency of expression is similar to that of humans. Various investigators have provided immunochemical evidence for IgG subclass and allotype diversity, although until the recent advent of molecular biology, the complete sequence of any swine immunoglobulin was unknown. Molecular genetic studies reveal single copies of C alpha and C epsilon but as many as eight copies of C gamma. The sequences of five IgG subclasses, IgG1, IgG2a, IgG2b, IgG3 and IgG4, are now available as well as the sequence and genomic organization of C alpha and the sequence of C mu. Swine CH genes all appear to belong to a single small family very similar to human VHIII. Especially interesting is the high degree of similarity among human and swine Ig genes despite the distinct phylogenetic relationship of these species. The rapid expansion of knowledge and technology in the field of molecular biology, together with the attractiveness of the swine as a model for immunoontogeny, in which the influences of both maternal regulatory factors and intestinal gut flora can be experimentally controlled, promises the beginning of an exciting area in swine immunology.