CD4, CD8 and TCR defined T-cell subsets in thymus and spleen of 2- and 7-week old commercial broiler chickens

To better understand immune development and function in meat-type chickens (broilers), the proportions of T-cells expressing CD4, CD8, and T-cell receptors (TCR) in the thymus and spleen were determined by three-color fluorescence and flow cytometry in 2- and 7-week old broilers raised in commercial growing conditions. Broiler thymocytes consisted of single-(CD4+CD8− and CD4−CD8+) and double-(CD4+CD8+) positive subpopulations. Within these CD4+ and/or CD8+ thymocyte populations, all types of TCR (yδ, Vβ1 αβ, and Vβ2 αβ) could be identified. In the thymus, percentages of CD4+CD8− cells increased, CD4−CD8+ cells remained unchanged, and CD4+CD8+ cells decreased between 2 and 7 weeks of age. In the spleen, in addition to single-positive lymphocytes, double-positive populations were identified, expressing either yδ or αβ TCR. The percentage of CD4+CD8− splenocytes decreased, and the percentages of both CD4−CD8+ and CD4+CD8+ splenocytes increased between 2 and 7 weeks of age. Age-associated shifts in TCR usage (the proportion of cells expressing a certain type of TCR) were observed in the single-positive, but not in the double-positive, T-cell populations of both thymus and spleen. This multiparameter cell population analysis in broilers demonstrates thymic and splenic T-cell subsets similar to those previously described in layers. Differences in the proportions among T-cell subsets between 2- and 7-week old broilers likely reflect a more competent immune system in the older birds.