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ES materials released along with the release of mf showed immunosuppression as evidenced by a decrease in T =ymphocyte levels in the immunised animals. Lipid fractions of the mf associated ES materials and protein fractions of the detergent soluble materials were fuund to cause suppression of immune response in the host. Further study revealed that the suppression associated with the lipid fractions is actually the end result and that mf associated ES materials is actually a mixture of immunosuppressive and immunopotentiating components and the release of the components is most likely regulated. KEY WORDS : Setaria digitata, Excretory Secretory materials, Immunopotentiation ImmunosuppressionFiladasis is a chronic infection in which host and parasite establish a fairly stable relation for many years. Inorder to survive, the parasite must be able to survive in a sensitised host. Filarial worms are considered to accomplish this by actively stimulating their host's normal regulatory mechanism and at the same time suppressing those immune reactions directed against them. Clear evidence to these speculations including the agents that might be responsible for these phenomena are still lacking. Filariae release a variety of molecules into the host environment, which are collectively called excretory secretory (ES) materials. ES materials released by living organisms have been shown to be highly immunogenic molecules in many nematode-infections (1). ES materials most probably arise from a variety of anatomical sources, including specialised structures, such as the intestinal tract and the parasitic cuticle where there is turnover of surface components. They may constitute the majority of ES products. In the case of adult filariae and microfilariae (mf), ES products include a complex mixture of shed surface molecules and materials released during the hatching of embryo. The importance of ES materials from parasites are widely accepted today both in reAddress for correspondence : Dr. R. Kaleysa Raj, at above address. lation to diagnosis and in immunisation in diseases such as Chagas disease, Toxocariasis, Onchocerciasis and Bancroftian filariasis. Working with a model filadal system, the S. digitata, Kaieysa Raj and group showed recently that the major source of ES materials is the materials released during the hatching process for the release of mf (2). and that the antigenicity of the ES products is proportional to the development of embryo to mf (3). The main problem in studies using materials of parasites of humans is its nonavailability and hence attention has been turned to heterologous materials derived from similar parasites to different hosts. In fact S. digitata is a cattle filarial parasite recommended by WHO as a model system for studies on experimental filariasis. EFFECT OF HATCHING ASSOCIATED MATERIALSES materials for immunological studies were separated from the incubation medium after incubating the So digitata under in vitro conditions in Tyrode medium at 37~ for a period of 4 hr using 2 ml per wor...