First evidence of gender-related differences in immune parameters of the clam Ruditapes philippinarum (Mollusca, Bivalvia).

For the Wrst time, gender-related diVerences in some important functional parameters of haemocytes from the clam Ruditapes philippinarum have been studied. Clams were collected during the pre-spawning phase, when sex can be distinguished by microscopic observation of gonadal smears, in order to ascertain whether the two sexes reach the stressful spawning period with diVerent degrees of immunosurveillance. Total haemocyte count (THC), haemocyte size frequency distribution, capability of haemocytes to assume the vital dye neutral red (NR, indicative of endocytotic activity), lysozyme-like and acid phosphatase activities in both haemocyte lysate (HL) and cell-free haemolymph (CFH), and superoxide dismutase (SOD) and catalase (CAT) activities in HL were all evaluated. No diVerences in THC values were found between the two sexes, but diVering haemocyte size frequency distributions were observed: the fraction of larger haemocytes (7–9 m diameter, 200 X volume) was markedly increased in females and that of smaller haemocytes (<5 m diameter, <200 X volume) markedly increased in males. Interestingly, when haemocytes were observed under the light microscope, a signiWcantly higher percentage of granulocytes was found in haemolymph from females, compared with that of males. SigniWcantly increased NR uptake was recorded in female haemocytes. No signiWcant variation in lysozyme-like activity was observed in HL, whereas in CFH, enzyme activity was signiWcantly higher in females. HL acid phosphatase activity was signiWcantly higher in males with respect to females; no signiWcant variations in enzyme activity were observed in CFH. HL SOD and CAT activities were signiWcantly higher in females than in males. Overall, on the basis of the cell parameters studied here, gender-related diVerences in immune parameters were found in R. philippinarum, indicating that females have more active haemocytes than males during the pre-spawning period.