Abstract
1. The purpose of this study was to investigate the distribution of Toll-like receptor-4 (TLR4) and major histocompatibility complex (MHC) class II molecules of the spleen in chicks treated with lipopolysaccharide (LPS) during the first 2 weeks of their life. 2. A total of 225 Ross-308 commercial broiler chicks were used. Within the 2-week experimental period, chicks were divided into 5 main groups according to the days of decapitation which were 1, 4, 7, 10 and 14 d after hatch. Each main group had 45 chicks. The main groups were further divided into three subgroups (15 chicks each), which included control chicks (no injection), and phosphate-buffered saline (PBS) and LPS-injected chicks. Spleen samples were collected 1-, 3-, 6-, 12- and 24-h after the PBS or LPS administrations. Tissue sections were stained using streptavidin-biotin-peroxidase complex staining method. 3. From 1 d of age, TLR4 positivity was found in the spleen in diffuse granular form. The cells showing intense TLR4 positivity were observed in periellipsoidal lymphoid tissue in 4-d-old chicks. The same cells were determined in the germinal centre of the spleen in 7-d-old chicks. LPS stimulation led to an increase in the intensity of TLR4 positivity in 14-d-old chicks. 4. From 1 d of age, MHC class II positivity was found in both white pulp and red pulp. This was higher in 14-d-old chicks injected with LPS than in the controls and the chicks injected with PBS. 5. The findings indicate that, from 1 d of age in chicks, the spleen has both non-specific defence elements and the molecules having the information to induce adaptive immunity. In addition, at the end of the 2-week experimental period, it was determined that the spleen had the capacity to recognise antigens.