Characterization of a secreted antigen of Onchocerca volvulus with host-protective potential

A cDNA designated MOv2 was isolated from an Onchocerca volvulus library on the basis of its product's recognition by an antiserum raised against the infective stage. Immunogold electron microscopy revealed a high density, of antigenic sites associated with the annulae of the L3 cuticle and with the uterine wall of the adult female: a general, low density of labelling occurred in all developmental for rns. Western blotting confirmed the presence nf the antigen throughout the life cycle and the existence of an immunologically, cross-reactive homologue in the related filaria, Acanthocheilonema viteae. The antigen was shown to be secreted by infective larvae and adult females of A. viteae. Sequence comparisons revealed two homologues of MOv2 (Ov-20, Ov-9) which had been selected independently by other laboratories on the basis of their specific recognition by human onchocerciasis infection sera. The IgG antibody response against MOv2 in cattle experimentally infected with O. lienalis revealed the indiction of a response during rite prepatent period that was strongly, boosted at the onset of patency. However, only a proportion of infected cattle responded with a detectable level of anti-MOv2 antibodies. The appearance of MOv2 in larval cuticle and secretions prompted us to evaluate it as a candidate molecule for prophylactic immunisation. Trials performed in the A. viteae/Mongolian jird model of filariasis revealed that recombinant MOv2 induced a host-protective response, reducing worm recoveries by 36-55% following a challenge infection.