In vitro effect of chitin particles on the innate cellular immune system of gilthead seabream (Sparus aurata L.).

The interaction between chitin particles and gilthead seabream (Sparus aurata L.) head-kidney leucocytes, as well as their effects on the main innate cellular immune responses were studied. Three different chitin particle-sizes were tested: unfiltered, <10 microM and >10 microM. Leucocytes were able to phagocytose only the chitin particles of <10 microM but not the >10 microM ones. Leucocytes were incubated with different concentrations (0 to 1000 microg ml(-1)) of the above chitin particles for 1, 4, 24 or 48 h and their effects on leucocyte viability and the innate cellular immune system were evaluated. Leucocytes incubated with chitin for 48 h maintained their viability as determined by the MTT viability test. Leucocyte phagocytosis of bacteria after chitin incubation for 1 or 4 h was enhanced by the highest chitin concentration tested of each of the chitin fractions studied, while the respiratory burst activity was unaffected. As regards leucocyte natural cytotoxic activity against tumour cells, prior incubation of leucocytes with chitin particles for 1 or 4 h increased while incubation for 24 or 48 h reduced the cytotoxic activity in a dose dependent manner. Statistically significant differences between the different chitin concentrations and between the three chitin particle-size fractions were detected. To conclude, gilthead seabream head-kidney leucocytes were able to phagocytose chitin particles smaller than 10 microM, and the main cellular innate immune activities were enhanced as a consequence of prior incubation with chitin particles.