Monoclonal antibodies that recognize distinct epitopes of the macrophage type three complement receptor differ in their ability to inhibit binding of Leishmania promastigotes harvested at different phases of their growth cycle.

The macrophage receptor CR3 has been shown by several investigators to be involved in the binding of Leishmania promastigotes to host macrophages. This receptor is known to recognize iC3b and to mediate direct lectin-like attachment of particles such as yeast zymosan. In the present study, two anti-CR3 monoclonal antibodies, M1/70 and 5C6, which ligate different epitopes of murine CR3, have been used in conjunction with sodium salicyl hydroxamate (Saha; inhibits covalent ester linkages of C3 to an activator surface) to block binding of L. donovani and L. major promastigotes harvested at different phases of their growth cycle. M1/70 inhibited all promastigote binding. 5C6 and Saha blocked in parallel only the binding of peanut agglutinin (PNA)-positive late log and early stationary phase parasites. These results suggest that the binding PNA-positive parasites to CR3 is iC3b-mediated, while entry of the more infective PNA-negative late stationary phase promastigotes into host macrophages may involve direct lectin-like binding to CR3.