Abstract
The posthatching development of lymphoid tissues and the distributions of immunoglobulin-containing cells (cIg: cIgG, cIgA, cIgM) or thymus-derived lymphocytes (T cells) which appeared in the upper alimentary tract (AT) and the respiratory tract (RT) of chickens were estimated immunohistochemically and histoplanimetrically. In adults, a marked amount of well-developed lymph nodules was noted in the upper AT as esophageal tonsils, and also in the RT as mesobronchial lymph nodules. Histoplanimetry showed the highest relative frequency in eacll class of cIg in the area of esophageal tonsils. A predominant frequency of cIgG compared to cIgA and cIgM was observed throughout upper AT and RT, and during the course of posthatching development, a small number of cIgG were found first in the esophageal tonsils and in the mesobronchial lymph nodules at 5 days of age. In these regions an active increase of cIgG was shown until 2 weeks of age, when the formation of germinal centers (GC) was first noted in the lymphoid tissues. In the lamina propria of the upper AT and RT, a large number of T cells appeared on the 20th day of incubation. And then the frequencies of cIg and T cells gradually increased with aging. These results suggested that the esophageal tonsils and the mesobronchial lymph nodules might act as local immune system corresponding to the Peyer's patches of cecal tonsils in the lower AT.
