TLR2 and TLR4 molecules and antigen-presenting cell compositions in cecal tonsils of broiler chicks (Gallus gallus domesticus) in the first two weeks of the post-hatch period

This study is a descriptive and experimental study that demonstrates the innate immunity and antigen presentation capacity of cecal tonsils of chicks. Cecal tonsils are an important part of gut-associated lymphoid tissue. The study was conducted to determine the histological development of the cecal tonsils and the distribution of Toll-like receptor (TLR) 2, TLR4 and antigen-presenting cells during the first 2 weeks of the chick's life. The tissue sections were stained using Crossmon's triple technique, Gordon and Sweet's silver impregnation, and streptavidin-biotin-peroxidase complex methods. A classical tonsil framework with fossa and tonsillar units were observed in 4 days cecal tissue. The web of reticular fibres forming the stroma of the tissue had the impression that the lymphoid cells filling in time. The development of cecal tonsil was completed histologically on the day 10 and following day 14 samples. Regardless of the antigenic stimulation, TLR2, TLR4 and CD83, major histocompatibility complex (MHC) class II molecules are present in proximal cecal tissue. However, CD83-positive dendritic cells in the germinal centre were first distinguished on day 7. Furthermore, the high antigen presentation capacity of the cecum with an intense MHC class II molecule expression was determined. Histological and immunohistochemical findings in this study revealed that both innate and adaptive cecal defence mechanisms were in the learning period during the first 2 weeks. The learning period of innate immunity may require more detailed research. However, the results obtained in this study will be taken into consideration in the vaccination programmes in chicks.

Automated summary

This study demonstrates the innate immunity and antigen presentation capacity of cecal tonsils in chicks, showing that regardless of antigenic stimulation, TLR2, TLR4, CD83, and MHC class II molecules are present in proximal cecal tissue. The development of cecal tonsil was completed histologically by day 10, with CD83-positive dendritic cells first distinguished on day 7. The results suggest that both innate and adaptive cecal defense mechanisms are in the learning period during the first 2 weeks, with potential implications for vaccination programs in chicks.