Seasonal changes in peripheral blood leukocyte functions of the turtle Mauremys caspica and their relationship with corticosterone, 17-beta-estradioland testosterone serum levels

We have studied the most representative functions of lymphocytes such as ad herence to substrate, mobility directed to a chemoattractant gradient (chem otaxis), proliferative response to mitogens and antibody-dependent cellular cytotoxicity (ADCC), as well as natural killer (NK) activity in peripheral blood cells from the turtle Mauremys caspica, and the seasonal changes of these functions in both female and male animals. The plasmatic levels of st eroid hormones were determined to study their relationship with the immune functions. Our results show high chemotaxis, lymphoproliferative response a nd ADCC as well as NK activity in winter when the levels of corticosterone, testosterone and 17-beta -estradiol were depleted. Proliferative responses to phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) were increased in spring correlating with low levels of corticosteron e and testosterone in middle and late spring. In summer, the proliferative response was decreased but adherence, chemotaxis, ADCC and NK activity were increased, although steroid hormones showed high plasmatic levels. In autu mn, a depletion of both the hormone levels and the immune response were fou nd except for adherence to substrate. The immune functions studied were str ikingly influenced by the seasonal cycle, which induced a different pattern of response depending on the function analyzed. Moreover, these immune cel ls showed a different degree of dependence on steroids in relation to the f unction and the season considered, suggesting the existence of other factor s that modulate the immune response studied. (C) 2000 Elsevier Science B.V. All rights reserved.