Plasma cells of the chicken Harderian gland

The chicken Harderian gland (HG) is densely populated in its subepithelial spaces with plasma cells (PC). These immune cells produce and secrete Ig of the IgA, IgG, and IgM classes. Such Ig secretion into the tears affords the upper respiratory tract with protective antibodies. The immunological role of the HG is quite interesting; yet this gland is a site of unusual PC proliferation. Studies of the gland utilizing bromodeoxyuridine (BrdUrd) incorporation into DNA and propidium iodide (PI) staining of PC DNA have verified previous suggestions in the literature that PC of the chicken HG proliferate. Both isolated PC suspensions and frozen sections of the HG from chicks aged 6 to 9 wk reveal that BrdUrd is incorporated into PC DNA. Furthermore, flow cytometric analysis of PI-stained PC indicates a relatively high percentage of PC in S phase of the cell cycle. Continued studies are examining possible mechanisms controlling proliferation and differentiation of PC in the HG. It is believed that the stromal elements of the HG produce and secrete a factor(s) that influences PC proliferation and differentiation. Isolation and characterization of this influencing factor(s) will allow for the possible systemic application of the factor(s) for enhancement of immune responses.