Pineal-Thymus Interrelation in Maintenance of T-Cell Dependent Immune Responses in a Tropical Seasonal Breeder Funambulus pennanti

Crosstalk between the neuro-endocrine axis and immune cells is documented in many laboratory and clinical studies. The pineal gland and its hormone melatonin play a central role in this network by positively regulating immune cell proliferation and differentiation via influencing the synthesis of immunomodulatory molecules. However, the pineal-thymus interaction in modulating their bi-directional communication remains elusive. In the present study we investigated the effect of pineal-thymus interaction on the structure and functional status of lymphoid tissues (i.e., spleen and lymph nodes) in a tropical seasonal breeder, F. pennanti. We observed that pinealectomy severely compromised the immune status of the squirrels. Besides pinealectomy, simultaneous ablation of pineal and thymus gland, further resulted in atrophy of the lymphoid tissues along with reduced total leucocyte and lymphocyte count. Exogenous melatonin administration improved the total leucocyte and lymphocyte count and restored T cell dependent immune responses and lymphoid tissue architecture in pinealectomized (Px) group. Our observations suggest that suppression of endogenous melatonin in Px group decreased the efficiency of the immune system probably by modulating the production of thymic factors, which becomes even severe with simultaneous ablation of the thymus and pineal gland, resulting in declined immune responsiveness. Thus, it can be inferred that the pineal melatonin and its interaction with thymus plays an important role in regulation of immune status of the squirrels.