The immune response of a marine teleost, Pseudopleuronectes americanus, (winter flounder) to the protozoan parasite Glugea stephani

Abstract

G. stephani is an intracellular cyst-forming microsporidan parasite that is found in the intestine of winter flounder (WF) Pseudopleuronectes americanus. No detectable humoral response was seen in parasitized fish or in fish injected with either spores or spore homogenate from this parasite. Quantification of total immunoglobulin (Ig) levels showed a decrease in Ig levels rather than enhancement, 21 days after intramuscular (IM) injections of spores (3×10 6/ml). When a second injection of spores was administered on day 21 and tested 3 weeks later, a further decrease in total serum Ig's occurred. A decrease in total IgM levels also occurred in WF that were simultaneously injected with G. stephani and the antigens, horse red blood cells (HRBC) or formalin-killed Klebsiella pneumonia (KP). The total Ig levels of fish injected with an antigen plus spores was not as low as those injected with the parasite alone. The Ig levels, as well as antibody titers to HRBC and KP were however, lower when compared to fish injected only with the HRBC or bacteria. Disrupted spore homogenate injected into winter flounder, showed a less marked decrease in Ig levels when compared with whole spores. When a single IM injection of spores was given, followed by two weekly injections of indomethacin (a drug that inhibits prostaglandin activity), no decrease in Ig levels occurred and levels were comparable to control (saline injected) fish.