Effect of migratory cycle and 17beta-estradiol on splenic leukocyte functions in female black-headed gulls

The immune function of wild birds is practically unknown. We have studied several functions of splenic leukocytes from the gull Larus ridibundus. Considering that avian physiology is strikingly affected by the seasonal migratory cycle, those functions were analyzed throughout the seasonal cycle. The functions assayed were: adherence to substrate, chemotaxis and lymphoproliferative response to mitogens. Estrogens have been reported to modulate the immune response in mammals; therefore serum levels of 17beta-estradiol were measured in order to find a putative effect of this hormone on the immune response of female gulls. According to our results, gull splenic leukocytes showed a response similar to that reported in mammals and poultry. In regard to the effect of the seasonal migratory cycle, when the gulls arrived from the migratory flight they showed an immunosuppression as we have obtained in chemotaxis and proliferations assays. The immune response increased during the resting period and especially in the premigratory period. We have found a lack of a direct effect of the age of the animals or even the serum estrogen levels in the immune response of the migratory gulls. These results suggest the existence of other hormones and releasing factors, which would modulate the immune response in gulls, or a unique major effect due to the long flight effort.