Lymphopoiesis in the chicken pineal gland

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Abstract
Pineal lymphoid development was studied in two breeds of chickens from hatching until sexual maturity. No lymphocytes were found in the pineal prior to 9 days of age (da). Lymphocytes migrate through the endothelium of venules into the pineal stroma. Lymphoid tissue reached its maximal accumulation in 32-da pineal glands of both breeds. At this age, the New Hampshire (NH) breed had a larger proportion of lymphoid volume to total pineal volume (32%) than did pineal glands from White Leghorn (WL) chickens (18%). Averaged over the period 23 to 62 da, NH chickens (a heavy breed) had a lymphoid volume (0.753 mm3) that was about three times greater (P < 0.05) than that of the lighter WL breed (0.251 mm3). Lymphocytes are able to enter cerebrospinal fluid from lymphoid accumulations (LA) embedded in the choroid plexus by migrating between choroid ependymal cells. The 122-da chickens typically lacked lymphoid tissue in the pineal gland with the exception of occasional LA contained in capsular tissue. Surgical bursectomy, thymectomy, or their combination at hatching followed with whole-body irradiation (IR) at 24 hours postsurgery inhibited the initial influx of lymphocytes usually seen in 9-da pineal glands. Also, these treatments prevented formation of germinal centers normally found in the pineal at 3 and 5 weeks and reduced total pineal volume at each age examined. However, pineal lymphoid volume of the surgical-IR group did not differ from control-IR chickens at either 3 or 5 weeks. Pineal glands from birds made agammaglobulinemic (bursa-cell depleted) by cyclophosphamide treatment in ovo were devoid of germinal centers, although thin strands of lymphocytes were usually found along venous sinuses. These dissociation studies suggest that the normal expression of lymphoid tissue in the chicken pineal gland is dependent on the bursa and thymus. Furthermore, these observations indicate that the pineal gland should be considered a functional component of the chicken's lymphomyeloid complex.