Serum immunoglobulin, dermal response, and lymphocyte transformation studies in horses with chronic diarrhea.

Serum specimens from 12 sick and 20 normal horses were examined for levels of different classes of immunoglobulin (Ig) by a single radial immunodiffusion. The level of IgA in the sera of sick horses was about 50% lower than in the sera of normal horses. By contrast, the level of serum IgG was higher in sick than in normal horses. Phytohemagglutinin (PHA) responsiveness of blood lymphocytes showed transient suppression during the stage of severe diarrhea. The regaining of PHA responsiveness of lymphocytes was observed simultaneously with the recovery process. However, the responsiveness of lymphocytes in recovered horses was still markedly lower than in normal horses. Allergic reactions in sick and normal horses were studied by observing dermal response to the injections of saline extracts from some of the horse feeds. A delayed hypersensitivity reaction to streptokinase-streptodornase and PHA was also studied. The allergic reactions to these extracts were not induced in either sick or normal horses; however, inflammatory response to the extracts was about 50% greater in normal than sick horses. Response to the intradermal injection, either streptokinase-streptodornase or PHA, was significantly greater in normal horses than sick horses. These findings are discussed with respect to the pathogenesis of chronic diarrhea and the complexity of immunodeficiency demonstrated in this disease. The possibility that transient defects of cell-mediated immunity may predispose to chronic diarrhea is proposed.