Objective—To characterize changes in lymphocyte
subsets over time in foals from birth to 18 weeks of
age, accounting for differences among individuals, and
to determine the effect of overnight storage of blood
samples on foal lymphocyte subset concentrations.
Animals—8 healthy Quarter Horse foals from birth to
18 weeks of age.
Procedure—Blood samples were collected longitudinally
from birth to 18 weeks of age and a CBC performed
on each sample. The samples were stained
for lymphocyte markers, either immediately or after
overnight storage and analyzed by flow cytometry.
Results—Total leukocytes, total lymphocytes, and
the absolute concentrations of all lymphocyte subsets
increased significantly with age. The proportions
of B29A+, CD21+, and equine major histocompatability
complex class-II molecule+ lymphocytes
increased significantly with age. The proportion of
equine (Eq) CD5+, EqCD8+, and EqWC4+ lymphocytes
decreased significantly with age. Significant differences
among foals were found with respect to initial
concentrations with respect to initial concentrations,
but not with respect to the rate of increase of the various
subsets tested. Significant differences were not
found in subset values when comparing blood samples
stained on the day of collection or after
overnight storage at room temperature (approx 21 C)
or under refrigeration.
Conclusions and Clinical Relevance—These results
are consistent with an increase in subset numbers
and proportions over time, but with individual differences
among foals. The observation of individual differences
in subsets among foals suggests that there
may be individual differences in susceptibility to infectious
disease during the perinatal period. The absence
of an effect of overnight storage makes field studies
of lymphocyte subset concentrations more feasible.
(Am J Vet Res 2002;63:531–537)