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

Dianne McFarlane DVM, MS1,2, Debra C. Sellon DVM, PhD3,4, and Scott A. Gibbs DVM5
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  • 1 Department of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.
  • | 2 Present Address is Department of Health Management, Atlantic Veterinary College, Univesity of Prince Edward Island,Charlottetown,Canada.
  • | 3 Department of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.
  • | 4 Present Address is Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, Wash.
  • | 5 Department of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

Abstract

Objective—To characterize age-associated changes in lymphocyte population subsets and immunoglobulin isotypes.

Animals—30 healthy young light-breed horses (5 to 12 years old) and 30 healthy aged light-breed horses (> 20 years old).

Procedure—Lymphocyte subset populations were identified, using monoclonal antibodies to cell surface markers CD5, CD4, CD8, and IgG. Subset populations were quantitated by use of flow cytometric analysis of antibody-stained cells. 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), IgM, or IgA did not differ with age.

Conclusions and Clinical Relevance—In horses, total lymphocyte count and lymphocyte subset cell counts decrease with age. Age-matched control values are necessary for optimal evaluation of hematologic variables in aged horses. The decrease in lymphocyte subset cell counts in healthy aged horses mimics that seen in other species and may contribute to an age-associated decrease in immunocompetency. ( Am J Vet Res 2001;62:1413–1417)

Abstract

Objective—To characterize age-associated changes in lymphocyte population subsets and immunoglobulin isotypes.

Animals—30 healthy young light-breed horses (5 to 12 years old) and 30 healthy aged light-breed horses (> 20 years old).

Procedure—Lymphocyte subset populations were identified, using monoclonal antibodies to cell surface markers CD5, CD4, CD8, and IgG. Subset populations were quantitated by use of flow cytometric analysis of antibody-stained cells. 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), IgM, or IgA did not differ with age.

Conclusions and Clinical Relevance—In horses, total lymphocyte count and lymphocyte subset cell counts decrease with age. Age-matched control values are necessary for optimal evaluation of hematologic variables in aged horses. The decrease in lymphocyte subset cell counts in healthy aged horses mimics that seen in other species and may contribute to an age-associated decrease in immunocompetency. ( Am J Vet Res 2001;62:1413–1417)