IMMUNOPHENOTYPIC ANALYSIS OF FOAL BRONCHOALVEOLAR LAVAGE LYMPHOCYTES

The purpose of this study was to define the normal immunophenotype of equine lymphocytes present within the pulmonary air spaces, and to det ermine if this changes as foals age from one to ten weeks. Six pairs o f mares and foals underwent sequential bronchoalveolar lavage (BAL) be tween 1 and 10 weeks of age. Data were grouped according to foal age ( 1, 1-3, 3-6, or 6-10 weeks of age) and were compared to adult control values obtained from the mares. BAL cells were harvested and stained w ith antibodies to the equine homologues of CD5, CD4, CD8, CD44, MHC I, MHC II and to equine IgG. Data, including percent positive staining a nd mean fluorescence intensity, were acquired on a flow cytometer gate d for viable lymphocytes. All foals had significantly fewer CD5(+) lym phocytes than mares, with the largest differences in the youngest anim als. The percentage of CD4(+) lymphocytes increased as the foals aged, approaching adult levels by 3 weeks of age, while the percentage of C D8(+) lymphocytes increased more slowly and approached adult levels by 10 weeks of age. The CD4:CD8 ratio changed from 1.26 at one week of a ge to 0.78 by 10 weeks of age, compared to an adult value of 0.66, Lym phocytes from foals less than 6 weeks of age expressed MHC II and CD44 at lower levels than adults. The lymphocytic populations within the a irways of foals are significantly different from adult animals. This m ay account for the susceptibility of foals to certain respiratory infe ctions during the first few months of life. (C) 1997 Elsevier Science B.V.