Immune cell proliferation in the harderian gland: an avian model

Experimentation has been carried out to study proliferation of plasma cells in the chicken Harderian gland (HG) and to determine if a HG factor influences immune cell (i.e., B cell) proliferation. In young chickens, flow cytometric analysis of propidium iodide (PI)-stained plasma cells revealed that the percentages of cells in both the synthetic (S) and mitotic (G2M) phases of the cell cycle were highest between 6 and 9 weeks of age. A pattern of plasma cell depletion and repopulation in the HG was observed following administration of emetine dihydrochloride. At 3 and 5 days posttreatment the plasma cell population decreased, and by 7 days posttreatment repopulation of the gland with plasma cells occurred. This repopulation appeared as a result of plasma cell proliferation within the HG. Anti-5-bromo-2'-deoxyuridine (BrdUrd) staining of frozen sections showed that the numbers of plasma cells incorporating BrdUrd were low at 3 days posttreatment but were as high, or higher than, controls at 5 and 7 days posttreatment. These results were verified with flow cytometric data of PI-stained plasma cells. Data from bursal cell bioassays revealed proliferative activity influenced by a HG factor. Coculture of bursal cells with phorbol dibutyrate and diluted HG supernatants resulted in prolonged and increased proliferation of these cells. It is possible that the HG of chickens supports plasma cell proliferation through the elaboration of a factor which acts like a lymphokine.