---

Aims and background: This study was performed to evaluate the effect of lactobacillus acidophilus Bacteria (LAB) on chicken T cell subsets at ileum, bursa and cecal tonsil tissues.
Material and Methods: Thirty chickens were divided into three groups and fed with sterilized cow milk (M), or a mixture of M and LAB, kept as controls. Chickens from each group were sacrificed after 2 or 3 weeks and lymphoid tissues including ileum, bursa and cecal tonsil were removed and cryo preserved. The ratio of T cell subsets including CD4+, CD8+ and gamma delta T cells were studied by immune-histochemistry method.
Results: The ratio of CD4+ T cells was significantly higher in ileum of chicken after 2 weeks of probiotic intake. Moreover, this ratio was even higher than the ratio of these cells in the third week. In the cecal tonsil sections the percentage of gamma delta T cells was higher in milk fed chickens, after 3 weeks.
conclusion: The findings indicate that feeding of chickens with probiotics may alter the distribution of T cells in the lymphoid tissues. However, coincidental increase of CD4+ and gamma delta T cells after 2 and 3 weeks of treatment indicates that these effects are transient and could not have a permanent effect on avian mucosal immunity.