Investigation of the distribution of MHC II molecules and TLR4 in spleen of broiler chicks

The purpose of the present study was to investigate histological development and distribution of TLR4 and MHC II molecules in the spleen of control and LPS stimulated groups within the first two weeks of life. A total of 225 Ross-308 commercial broiler chicks were used. The chicks were divided into 5 main groups (age: 1, 4, 7, 10 and 14 days), each group had 45 chicks. Each main group was divided into three subgroups which included control (conventional), PBS and LPS-injected groups. Antigenic stimulation was carried out through intra-abdominal (i.a.) administration of LPS at a dosage of 1mg/kg. Tissue samples in the subgroups were collected separately at 1, 3, 6, 12, and 24h after LPS or PBS injection. At the same time, tissue samples were obtained from three animals in the control group. Tissue sections were stained using triple staining, Gordon and Sweet's silver staining. Furthermore, orcein–giemsa methods as well as immunohistochemistry were performed to determine the expression of TLR4 and MHC II molecules. Histological development of the spleen was recorded between one and 14 days. Granulopoesis was observed in the chicks until the age of 4 days. Between 1-14 days of age, a diffused expression of TLR4 was found in the tissue but generally in red pulp, some cells showed strong expression. Whereas, some cells showed intense TLR4 expression in PEL and GC, at the age of 4th and 7th day, respectively. Variations in the statistical evaluation were found in diffused granular expression of TLR4 density on different days. The number of dense positive cells was increased again by antigenic stimulation in 14 days old chicks. Besides the non-specific defense cells, TLR4 expression was also observed in endothelial and smooth muscle cells. MHC II molecules were diffusely observed at SCL, PAL, PEL, PVL, GC and red pulp from post-hatch day one onwards. It was noticed that the control group had lesser expression of TLR4 as compared to other groups on daily basis. Moreover, it increased after LPS stimulation at one and 14 days of age. It is suggested that spleen has nonspecific defense processes from post-hatch day one onwards. Functional splenic development is completed histologically at 14 days of age. It is suggested that TLR4 and MHC II positivity must be examined in the spleen on the basis of cell types with further research.