Age-related quantitative alterations in lymphocyte subsets and immunoglobulin isotypes in healthy horses

Objective-To characterize age-associated changes in lymphocyte population s ubsets and immunoglobulin isotypes. Animals-30 healthy young light-breed horses (5 to 12 years old) and 30 heal thy aged light-breed horses (> 20 years old). Procedure-Lymphocyte subset populations were identified, using monoclonal a ntibodies to cell surface markers CD5, CD4, CD8, and IgG. Subset population s were quantitated by use of flow cytometric analysis of antibody-stained c ells. Serum immunoglobulin concentration was determined using single radial immunodiffusion. Results-Absolute cell counts of total lymphocytes, T cells, CD4(+) and CD8( +) T cells, and B cells were decreased in aged horses, compared with young horses. There was a significant decrease in the percentage of CD8(+) cells and an increase In the CD4(+)-to-CD8(+) cell ratio In the aged population, compared with young horses. However, serum concentration of IgG, IgG(T), Ig M, or IgA did not differ with age. Conclusions and Clinical Relevance-In horses, total lymphocyte count and ly mphocyte subset cell counts decrease with age. Age-matched control values a re necessary for optimal evaluation of hematologic variables In aged horses . The decrease in lymphocyte subset cell counts in healthy aged horses mimi cs that seen in other species and may contribute to an age-associated decre ase in immunocompetency.