Assessment of lymphocyte subsets is an effective method for characterizing disorders
such as leukemia, lymphomas, autoimmune and infectious diseases. In order to clinically
interpret these parameters, normal reference values should be set, estimating age-
and gender-related variations. This research aimed to: (1) characterize lymphocyte
subpopulations in Andalusian horse, and (2) evaluate age and gender-related variations
of lymphocyte subsets. Jugular blood samples were obtained from 159 animals, 77 males
and 82 females, belonging to four age groups-1: 1-2 years (N=39; 21 males and 18 females),
2: 2-3 years (N=38; 16 males and 22 females), 3: 3-4 years (N=41; 19 males and 22
females) and 4: 4-7 years (N=41; 21 males and 20 females). T lymphocytes subsets were
quantified by flow cytometry with monoclonal antibodies specific for CD2, CD4 and
CD8 cell markers. B and NK cell counts were estimated by using a mathematical formula.
No variations were found in T, B lymphocytes and NK cells between males and females.
Animals of group 1 and 2 had a higher number of CD2, T, CD4+, CD8+, B lymphocytes
and NK cells than animals of groups 3 and 4. The percentage of CD2 in group 1 was
significantly lower than in group 4. The percentage of T and CD4+ lymphocytes in the
group 1 were significantly higher than groups 2 and 3, respectively. Whereas the percentage
of B cells calculated by flow cytometry was significantly lower in group 2 compared
to group 4, the percentage of B cells calculated by a mathematical formula was higher
in group 1. NK cells percentage was significantly lower in group 3 and 4 than in younger
animals. In conclusion, in Andalusian horse, gender does not influence absolute numbers
and percentages of T, B and NK. There is an age-related decline in absolute number
of CD2, T, CD4+ and CD8+ lymphocytes, B lymphocytes and NK cells, with increasing
percentage of CD2, T, CD4+ and B lymphocytes, and a decrease in NK with no differences
in CD4/CD8 ratio. The decline of lymphocyte population numbers with age is a natural
process in many animal species, and could be the origin for immune dysfunction observed
in geriatric individuals.