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