Immunisation of mice with fractions derived from the intestines of Dirofilaria immitis.

Antigens that are not normally seen by the host but that are nevertheless, accessible to host immune effector molecules and cells such as the native endoantigens associated with the intestinal epithelium of haematophagous tissue-dwelling parasites, could be potentially useful vaccine antigens. In this study, intestines were dissected from adult Dirofilaria immitis, homogenised, and a 105,000 x g pellet obtained and extracted with Triton X-100. The soluble 105,000 x g supernatant from this extract induced partial protection (51%) against a challenge infection of third stage larvae (L3) implanted in micropore chambers. Sera from mice immunised with this soluble detergent extract reacted with proteins ranging in size from 38 to 130 kDa. Immunolocalisation studies indicated the mouse sera reacted primarily to the lumenal surface of the intestines of adult D. immitis, though reactivity to the lateral nerve/epithelial chords, hypodermis and reproductive tracts was also noted, indicating the presence of shared antigens. Tissues of L3s were also recognised by the immunised mouse sera. These mouse sera did not react to a dog blood fraction prepared identically to the D. immitis fraction. Only those sera from D. immitis-infected dogs with heavy or long-term infections were reactive to a single 42 kDa protein. After 24 h incubation in fluorescein isothiocyanate-conjugated serum the intestinal tract of Onchocerca volvulus and D. immitis L3 and L4 fluoresced, indicating the serum had been ingested. These data suggest that filarial gut-associated antigens (apart from the single 42 kDa antigen) are not seen by normally infected hosts, that they can be accessible to antibodies and that they can induce an immune response which is partially protective.