Role of Excretory–Secretory Metabolites of Fasciola gigantica in Modulating Delayed-type Hypersensitivity in Rats

The role of excretory–secretory metabolites of Fasciola gigantica in modulating the delayed type of hypersensitivity in the host (rats) was investigated. Eighteen rats of either sex, aged 3–4 months, were assigned to three groups of 6 animals each. Rats in group 1 served as non-inoculated controls and each rat in this group was administered only Freund's complete adjuvant on day 7. Animals in groups 2 and 3 were administered inoculation dose(s) of somatic F. gigantica antigen (SFgA) and excretory–secretory F. gigantica antigens (ESFgA) according to the experimental schedule. The delayed-type hypersensitivity was monitored by assessing alterations in the foot pad thickness, its histopathology and lymphocyte proliferation assay. It was observed that the ESFgA caused diminution in delayed-type hypersensitivity response to a significant level (p<0.01) against SFgA in rats. This finding was further confirmed by lower stimulation indices of peripheral blood mononuclear cell in rats sensitized with ESFgA prior to inoculation of SFgA (group 1) than in nonsensitized rats receiving only SFgA (group 2).