Immunologic aspects of combined immunodeficiency disease in Arabian foals

Tests for T- and B-cell quantitation and immune function were developed, and their application in the diagnosis of primary severe combined immunodeficiency disease (CID) in Arabian foals was investigated. Foals with CID had severe lymphopenia and had small or zero numbers of B cells, as shown by immunofluorescence of surface immunoglobulin (Ig), erythrocyte-antibody-complement rosetting, and staphylococcal protein A rosetting. Serum IgM was undetectable in four CID foals 25 to 71 days old. Demonstrable antibody responses were not elicited in CID foals by phage phi X-174, a potent antigen in normal foals. Nonspecific esterase (NSE) staining in the pattern of a single vesicle was investigated as a possible marker for equine T cells. For normal foals, 64.0% of peripheral blood lymphocytes stained NSE positive. The CID foal 1 had only 4.0% NSE-positive lymphocytes, whereas CID foals 2, 3, and 4 had 75%, 68%, and 77.5%, respectively. In an in vitro T-cell function test, lymphocytes from 12 normal foals did not show a response. In normal foals, intradermal injection of 50 micrograms of phytohemagglutinin induced visible reactions, and skin grafting induced a pronounced mononuclear cell response at the base of the graft. In contrast, there was little or no response in the foals with CID.