DIFFERENTIAL RECOGNITION OF MICROFILARIAL CHITINASE, A TRANSMISSION-BLOCKING VACCINE CANDIDATE ANTIGEN, BY SERA FROM PATIENTS WITH BRUGIAN AND BANCROFTIAN FILARIASIS

We examined the reactivity of human sera with recombinant microfilaria l chitinase and with the anti genic determinant on the native parasite molecule identified by monoclonal antibody (MAb) MF1. In Brugian fila riasis, the MF1 epitope is preferentially recognized by residents of e ndemic areas who remain amicrofilaremic and asymptomatic despite lifel ong exposure to filarial worms. Reactivity with filarial chitinase and its MF1 epitope inversely correlates with microfilaremia levels in Ba ncroftian filariasis and is associated with a prolonged amicrofilaremi c state following a single course of treatment with diethylcarbamazine . Chitinase does not appear to be a target of human antibodies that pr omote the adherence of cells to microfilariae, even though MAb MF1 its elf promotes antibody-dependent, cell-mediated cytotoxic (ADCC) reacti ons that kill microfilariae in vitro. Such ADCC reactions are most oft en mediated by sera from amicrofilaremic patients with chronic elephan tiasis that contain low or undetectable levels of IgG antibodies to ch itinase. In contrast, antibodies to the MF1 epitope on this microfilar ial stage-specific antigen are mostly present in amicrofilaremic donor s without clinical lymphatic disease. These observations indicate that antibodies to the MF1 epitope of microfilarial chitinase reflect some degree of immune resistance to microfilaremia in a subgroup of patien ts with asymptomatic lymphatic filariasis. The amicrofilaremic state o f individuals with chronic lymphatic disease appears to be mediated by reactivity to a different parasite antigen(s).