Attachment of plasma membrane vesicles of human macrophages to Leishmania tropica promastigotes.

Intracellular parasitism of host macrophages is the pathologic hallmark of leishmaniasis. Since the organisms are found almost exclusively in this type of cell, the possibility that specific macrophage plasma-membrane determinants mediate the attachment to promastigotes of Leishmania tropica was investigated. Plasma membrane vesicles were prepared from human monocytes/macrophages and erythrocytes, radioiodinated, and incubated with L tropica promastigotes, erythrocytes, or Sephadex beads. Macrophage plasma-membrane vesicles bound to promastigotes to a significant extent but did not bind to intact erythrocytes or to an inert particle. In contrast, erythrocyte membrane vesicles did not bind to promastigotes. The binding of macrophage plasma-membrane vesicles to promastigotes demonstrated the characteristics of a receptor-ligand interaction in terms of specificity, saturability, competitive inhibition, and temperature independence. These results suggest the presence of one or more intrinsic binding sites on the macrophage plasma membrane to which promastigotes can attach. If this is the case, therapeutic intervention by strategies that inhibit attachment of this obligate intracellular parasite to its target host cell may be possible.