A sensitive method for assaying chemotaxic responses of Leishmania promastigotes

This article describes a sensitive, cheap, and easy method for assaying che motaxic responses of Leishmania promastigotes. A gradient of the substance to be assayed was produced inside a series of commercially available capill ary tubes submerged in a promastigote suspension. After an incubation perio d, the attractiveness of the substance under test was measured by counting the number of parasites in the capillaries in a Neubauer chamber. Different responses were detected in two strains of Leishmania amazonensis and one s train of L, chagasi after standardization of the method to assay attraction to carbohydrates. Very different responses were obtained when the test was performed using promastigotes of the same strain in two different physiolo gical states (log and stationary phase). The stationary phase cells showed an enhanced chemotaxic capability, which can be explained by the fact that the metacyclic forms commonest in stationary phase cultures have greater mo bility than other promastigotes. This method will permit studies to be made of the attractive response to different substances in Leishmania species a nd other trypanosomatids and facilitate characterization of the potential r eceptors involved in the chemotaxic response. An adaptation of the method t o assay the response to repellent substances is also provided. (C) 2000 Aca demic Press.