The Serum and Secretory Immunoglobulins of Cattle: Characterization and Quantitation

Abstract

Immunoglobulins in bovine serum and in lacteal, salivary, nasal and vaginal secretions have been characterized on the basis of antigenic distinctions, ion exchange and gel filtration properties, and ultracentrifugal analysis. IgG₁, IgG₂, IgM and IgA have been clearly distinguished and the presence of a secretory IgA system analogous to that in other mammalian species has been confirmed. All detectable bovine serum IgA has a molecular weight consonant with its existence in dimeric form. The quantitative distribution of immunoglobulins and albumin were measured in serum and nasal, lacrimal, salivary and vaginal secretions of four heifers for 9- to 12-week periods. IgA is a minor serum component but is the predominant immunoglobulin in nasal secretions, tears and saliva; in vaginal mucus its relative concentration is lower than IgG but still much higher proportionally than in serum. Marked weekly fluctuations occurred in each secretion in IgA/total protein ratios. IgG₁ was consistently the predominant IgG subclass in each secretion although the serum relationship varied among animals. With two exceptions a significant positive correlation existed between IgG and albumin in every secretion. IgM levels in secretions were generally low but in two parenterally immunized heifers mean IgM concentrations in nasal secretions exceeded those of IgG. Local synthesis or selective transport must account for virtually all of the IgA as well as a portion of IgG₁ and, possibly, IgM in these secretions. Serum components derived by transudation account for a much higher proportion of total protein in vaginal mucus than in nasal, lacrimal, or salivary secretions.