B cells and T-lymphocyte subsets of the head-associated lymphoid tissues of the chicken.

The head-associated lymphoid tissues of the chicken, composed of the harderian gland and the conjunctiva-associated lymphoid tissue (CALT), were studied to determine whether changes occurred in lymphocyte subpopulations as chickens age from 1 week to 8 weeks. The B cells and subpopulations of T-lymphocytes of the head-associated lymphoid tissues were identified using in situ immunohistochemical staining. Monoclonal antibodies specific for various lymphocyte surface antigens were used. The concentration of T-lymphocytes, particularly CD3+ and CD4+ cells, within the harderian gland increased with age, whereas the concentration of B cells remained the same. B-lymphocytes were observed within the germinal centers of the CALT of 4-week-old birds. The T-lymphocytes within the CALT surrounded the B-cell-rich germinal centers. CD3+ T-lymphocytes were the predominant cell population in all age groups examined. Increasing concentrations of CD3+, CD4+, and CD8+ T-lymphocytes were observed within the CALT as chicks developed from 1 week to 4 weeks of age. Finally, no changes were observed in lymphocyte populations within the CALT as chicks developed from 4 weeks to 8 weeks of age.