The influence of antibiotics on B-cell number, percentage, and distribution in the bursa of Fabricius of newly hatched chicks.

Antibiotics are commonly used to prevent and treat poultry microbial infections, but certain antibiotic families depress humoral immunity, such as antibody production. Poultry humoral immunity depends on the normal functioning of the bursa of Fabricius and the B lymphocytes that mature in that gland. In this study, recommended therapeutic doses of enrofloxacin, florfenicol, or ceftiofur were administered to 2-d-old chicks. On d 7 post-hatch, bursae were sampled for histological, immunohistochemical, and flow cytometric determination of Bu-1-positive (Bu-1+) cell number, percentage, and distribution. The bursa of Fabricius from all treatment and control groups had normal morphology. The administration of antibiotics significantly decreased the number of Bu-1+ cells in the bursal medulla, with a simultaneous increase of these cells in the cortex. Flow cytometry revealed a significant decrease in the percentage of bursal Bu-1+ cells from all of the studied antibiotics: enrofloxacin (93.91 ± 3.27), florfenicol (87.84 ± 7.14), and ceftiofur (89.16 ± 5.68) compared with that of the control (96.48 ± 2.60). The combination of reduced percentages of Bu-1+ cells and a decrease in these cells in the medullary region suggests lower B cell maturation.