Protection against L3 induced Brugia malayi infection in Mastomys coucha pre-immunized with BmAFII fraction of the filarial adult worm.

The present study was aimed at investigating protective efficacy of BmAFII (Sephadex G-200 eluted fraction of Brugia malayi adult worm extract) against establishment of infective larvae (L3)-induced B. malayi infection in Mastomys coucha and to delineate immunological responses induced in the host. Healthy male M. coucha were immunized with BmAFII and subsequently inoculated with B. malayi L3. Specific IgG and cell mediated immune responses (cellular proliferation) including release of tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), transforming growth factor-beta (TGF-beta) and nitric oxide (NO) from host's cells stimulated with BmAFII or lipopolysaccharide (LPS)/concanavalin A (Con A) in vitro were determined. Immunization with BmAFII reduced the adult worm recovery by 85.7% (P<0.001) and microfilaraemia by 77-95% of unimmunized controls (P<0.05-0.01). Immunization alone resulted in downregulation of responses of cellular proliferation, IFN-gamma, TNF-alpha and NO production (P<0.01) but increased TGF-beta release (P<0.001) whereas the converse was seen after L3 inoculation in these animals. In unimmunized+L3 inoculated animals all the above parameters were found downregulated (P<0.01-0.001). The cell proliferative response of BmAFII immunized+L3 challenged animals was larger for Con A (P<0.001) but not for BmAFII. Specific IgG levels were higher in immunized, immunized+L3 inoculated and unimmunized+L3 inoculated groups (P<0.001) compared to unimmunized animals, the highest level being shown by immunized+L3 inoculated group. In conclusion, immunization with BmAFII suppresses establishment of L3-induced infection in M. coucha by stimulating proinflammatory responses to L3.