Prostaglandins E2 and D2-regulators of host immunity in the model parasite Diphyllobothrium dendriticum: An immunocytochemical and biochemical study.

The spectrum of immunomodulating molecules produced by tapeworms is not yet well understood. The aims of this study, on the tapeworm Diphyllobothrium dendriticum, were: 1) detection and quantification of prostaglandins (PGs) E2 and D2 by high performance liquid chromatography; 2) visualization of PGE2 and PGD2 in specific cells, using methods of immunocytochemistry and confocal laser scanning microscopy; and 3) investigation of the ultrastructure of the cells potentially producing PGE2 and PGD2. The PGE2 immunoreaction (IR) was found in the apical terminals of the frontal glands and sensory organs in the tegument and in small neurons belonging to the main cords and commissures. PGE2-IR partly coincided with α-tubulin-IR. PGD2-IR occurred in the muscle fibers of longitudinal and transverse body muscles and coincided with phalloidin TRITC staining. Both PGE2 and PGD2 were found in the flame cells of the excretory system. Ultrastructural study of the tegument revealed two types of structures that potentially produce PGE2: ciliated and unciliated free nerve endings and frontal gland terminals reinforced with neurotubules. In the main nerve cords, small neurons were identified as potentially exhibiting PGE2-immunoreactivity. In homogenates of the plerocercoids, the measured content of PGE2 and PGD2 was 33.15ngmg-1 and 1.94ngmg-1 of fresh tissue weight, respectively. We found evidence of PGE2 and PGD2 in D. dendriticum parasitizing Coregonus autumnalis (fish) and proved excretion of PGE2 and PGD2 in response to C. autumnalis blood serum. Prostaglandins produced by D. dendriticum probably play a dual role: 1) PGE2 and PGD2 potentially modulate the fish antiparasitic immune response; 2) PGE2 is presumably necessary for proper development and function of the nervous system, and PGD2 can act as an antagonist against mediators causing muscle contraction.