Expression of Leishmania antigen on the surface membrane of infected human macrophages in vitro.

Resolution of leishmaniasis is associated with host immunological responsiveness to parasite antigens. In clinical disease, leishmania are found as amastigotes contained with macrophages. We investigated the possibility that Leishmania antigens are expressed on the infected macrophage surface by reacting infected macrophages with antibody to Leishmania. In vitro-infected human monocyte-derived macrophages were labelled with antibody to amastigotes when examined with immunofluorescent or immunoelectron microscopic techniques. Infected macrophages were poorly labelled by antibody to promastigotes (insect forms of Leishmania). Certain antisera that reacted with the surface membranes of amastigotes did not label the infected macrophage surface. These results indicate that human macrophages infected in vitro express Leishmania amastigote antigen(s) on their surface membranes, that such antigen(s) may not be present in large quantities in promastigotes, and that certain antigen(s) on the amastigote surface are not expressed on the surface membranes of infected macrophages.