Antibody-induced modulation of Leishmania donovani surface membrane antigens.

The effects of specific antibodies on the surface membrane antigens of Leishmania donovani (strain 1S, clone 2D) amastigote and promastigote developmental stages was detected in vitro by using several direct and indirect immunofluorescence methods. Stage specific anti-L. donovani sera and sera from L. donovani-infected hamsters induced parasite surface membrane antigens to aggregate, move along the longitudinal cell axis, form polar cell caps, and subsequently disappear. No membrane fluorescence was observed in cells treated identically with normal sera. In amastigotes in a single anterior cell pole cap was formed after antibody treatment. However, antibody-treated promastigotes showed tripartite membrane antigen capping consisting of a major anterior cell pole cap with minor caps at the posterior cell pole and flagellar tip regions. Loss of surface fluorescence from the two latter capped cell regions was frequently concurrent with the formation of extracellular fluorescent plasmanemes. The cell-capping process was antibody concentration, temperature, time, and energy dependent. No cell caps were formed at low temperature or in the presence of several metabolic inhibitors. Cell cap formation was also selectively inhibited by certain types of antibody-induced intercellular agglutination. Parasite membrane antigens removed by capping were regenerated and detectable at the cell surface only after a 3.5 to 4-hr period. Antibody-induced membrane antigen movement in L. donovani is apparently similar to pheonmena observed with mammalian cells. Results of direct cross-staining and cross-absorption cell-capping experiments showed that the two parasite developmental forms shared some common or at least cross-reacting membrane antigens and that each form also possessed some unique stage-specific surface antigens. Cell-capping results with sera from L. donovani infected hamsters showed that this host produces some IgG which is directed specifically against certain parasite surface membrane antigens. The results suggest that host antibody-induced parasite membrane antigen modulation might have a role in the infectious process of this human pathogen.