Respiratory burst assay of head kidney macrophages of ayu, Plecoglossus altivelis, stimulated with Glugea plecoglossi (Protozoa: Microspora) spores.

The respiratory burst assay was conducted using the nitroblue tetrazolium reduction method and horseradish peroxidase method to investigate the events when ayu head kidney macrophages phagocytize fresh and formalin-killed Glugea plecoglossi spores. The production of O2 against G. plecoglossi spores was negligible compared to zymosan (P < 0.01). Zymosan-induced O2 production was markedly inhibited by adding G. plecoglossi spores simultaneously (P < 0.01). This phenomenon was dose dependent, and killed spores were less inhibitory than fresh spores. The production of H2O2 was drastically increased when G. plecoglossi spores were added (P < 0.01), and most spores were phagocytized. From these results, it is suggested that G. plecoglossi spores modulate the host's phagocytic response to establish infection.