Immunoglobulin levels of the winter flounder (Pseudopleuronectes americanus) and the summer flounder (Paralichthys dentatus) injected with the microsporidan parasite Glugea stephani.

The microsporidan parasite G. stephani, has been found in the intestine of the American winter flounder Pseudopleuronectes americanus. A quantitative study of total serum immunoglobulin (Ig) levels has shown that an injection of this parasitic spore causes a decrease in serum IgM levels. The level of suppression seems to be related to the number of spores injected into the host, as well as the frequency of injections administered. As the dosage of spores injected into the winter flounder increased from 3 X 10(3)/ml to 3 X 10(8)/ml, the level of serum IgM's decreased proportionally. When a single IM injection of spores (3 X 10(6)/ml) was administered, the initial decrease in serum IgM was followed by a gradual recovery of total Ig levels by day 60. Repeated injections of G. stephani on days 21 and 42 respectively, causes an even greater decrease in total IgM levels. Indomethacin (a drug that inhibits prostaglandin activity), has been shown to negate the decrease in IgM levels caused by the G. stephani spores. When injected twice weekly, the indomethacin inhibited the decrease in serum IgM caused by the spore homogenate, with IgM levels comparable to those observed in control WF. This supports previous observations, that prostaglandins are implicated in the decrease in IgM levels induced by injection of the parasite. The effects of G. stephani on serum Ig levels does not seem to be species-specific. When the spores were injected into summer flounder (Paralichthys dentatus) together with an erythrocyte antigen, horse red blood cells (HRBC), a decrease in total IgM levels occurred, as well as a decrease in hemagglutination titers to HRBC similar to the decrease described in winter flounder.