GIARDIA-LAMBLIA VARIANT SURFACE PROTEIN H7 STIMULATES A HETEROGENEOUSREPERTOIRE OF ANTIBODIES DISPLAYING DIFFERENTIAL CYTOLOGICAL EFFECTS ON THE PARASITE

Previous investigations had shown that the Giardia lamblia clone GS/M- 83-H7-specific variant surface protein (VSP) H7 consists of at least t wo antigenically distinct parts: (i) a variable 314-aa N-terminal regi on which contains one, or more, variant-specific epitopes eliciting a transient and consequently low-level antibody response preferentially detectable during the early phase of a G. lamblia infection in mice; a nd (ii) a 171-aa C-terminal region which contains relatively conserved epitope(s) causing a persistent and consequently high-level antibody response during the later phase of an infection. The present study ind icated that monoclonal antibody G10/4 and polyclonal antibodies from e arly-phase infected or hyperimmunized mice, directed against the varia nt-specific N-terminal region, exclusively recognized conformational c ysteine-containing epitopes. These antibodies caused detachment and ag gregation of trophozoites, and exhibited complement-independent cytoto xic effect towards the parasite. In contrast, polyclonal antibodies fr om late-phase infected mice, directed against the semi-conserved pepti dyl structures in the C-terminal region, preferentially reacted with n on-conformational epitopes. Such antibodies had no cytotoxic effect, b ut provoked parasite-detachment and -aggregation. These findings indic ated that infection of mice with G. lamblia clone GS/M-83-H7 generates a heterogeneous repertoire of cytologically active anti-VSP H7 antibo dies which may have a direct influence on the course of the parasite i nfection. (C) 1997 Elsevier Science B.V.