Leishmania: Chemotaxic Responses of Promastigotes and Macrophages In Vitro1

Abstract

Promastigotes of Leshmania move progressively up a concentration gradient of: various sugars, specific sugars attracting individual species of Leishmania [L. mexicana mexicana from Nyctomys sumichrasti, L.major from Rhombomys opimus, L. donovani from Rattus rattus and L. tropica from man] serum albumin and another unidentified constituent of serum; Hb; and a factor generated by promastigotes in NNN medium. The movement of promastigotes up a concentration gradient of serum is optimal at a pH of 6.4-6.8 and a temperature .gtoreq. 28.degree. C. Cholinergic and adrenergic agents did not affect the attraction of serum for promastigotes, and cyclic nucleotides, inflammatory mediators and macrophage products were not chemotaxic. The sugar chemotaxins influence the movement of promastigotes from the sand fly midgut to the esophagus, and serum chemotaxins may play a part in the entry of promastigotes into the skin of a mammal from the proboscis. Macrophages, the host cell of the obligate intracellular Leishmania sp., were not attracted to any product of promastigotes. When promastigotes interact with serum, complement is activated to form [complement component] C5a which is chemotaxic for macrophages. Activation of complement by promastigotes is, at least partially, by the alternate pathway. Other chemotaxins resulting from promastigote interaction with serum may also be present. Promastigotes may also produce inhibitors of C5a activity.