Abstract
For the first time, gender-related differences 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 different 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 differences in THC values were found between the two sexes, but differing haemocyte size frequency distributions were observed: the fraction of larger haemocytes (7–9 μm diameter, 200 fl volume) was markedly increased in females and that of smaller haemocytes (<5 μm diameter, <200 fl volume) markedly increased in males. Interestingly, when haemocytes were observed under the light microscope, a significantly higher percentage of granulocytes was found in haemolymph from females, compared with that of males. Significantly increased NR uptake was recorded in female haemocytes. No significant variation in lysozyme-like activity was observed in HL, whereas in CFH, enzyme activity was significantly higher in females. HL acid phosphatase activity was significantly higher in males with respect to females; no significant variations in enzyme activity were observed in CFH. HL SOD and CAT activities were significantly higher in females than in males. Overall, on the basis of the cell parameters studied here, gender-related differences in immune parameters were found in R. philippinarum, indicating that females have more active haemocytes than males during the pre-spawning period.
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