Bovine Immunoglobulins: A Review

Abstract

Three classes of immunoglobulins have been identified in the cow: IgG, IgA, and Ig)~. The IgG immunoglobulins can be divided into two subclasses, IgG1 and IgG2. IgG1 is selectively transported by the udder from the circulation to the lac- teal secretions by a mechanism yet to be elucidated. Hence, IgG1 is the principal immunoglobulin for passive immunization of the calf. IgG1 also fixes complement and sensitizes bovine skin. IgG2 appears more homogeneous than IgG1 and occurs in high concentrations in bovine serum. Bovine IglV( occurs in serum, colostrum, and milk. IgM is important in the primary immune response, complement fixation, and as an agglutinating antibody of the serum. IgM seems to be especially associated with para- sitic infections of Anaplasma. Bovine IgA occurs as "secretory IgA" in milk and colostrum. Whether secretory IgA, or any other immunoglobulin, is synthesized lo- cally is unknown. Also unknown is the precise role that each immunoglobulin plays in bovine pathology. Transfer of immunity to the offspring is by way of the milk and colostrum, and there is sufficient evidence that colostrum is necessary for immunity to disease. Al- though IgG1 is selectively concentrated by the bovine mammary tissue, no selectivity has been demonstrated for the highly per- meable calf's gut. The reason for the fail- ure of some calves to absorb colostral immunoglobulins is unknown. Additional research endeavors into the distribution, genetics, function, and synthe- sis of the bovine immunoglobulins are most needed.