The effects of the antibacterial protein Drosophila cecropin A on developmental forms of Leishmania were compared with the effect of Hyalophora cecropin A in vitro. Both cecropins had a potent lytic activity on the promastigotes at concentrations not far from those occurring in vivo in the respective insect. Drosophila cecropin A had strong differential effects on the two maturation forms of Leishmania aethiopica at high concentrations: inhibiting intracellular amastigotes and stimulating extracellular promastigotes to take up thymidine. Hyalophora cecropin A also inhibited amastigotes by up to 50% at concentrations of 0.250 mg/ml, and inhibited promastigotes at high concentrations but had no enhancing effects at any of the concentrations tested. In contrast to the results with Leishmania, Drosophila cecropin A had no discernible effect on any developmental stage of P. falciparium and showed no lytic effects on haemocytes. The two enantiomers of a synthetic amphipathic peptide, D- and L-KALA, were also tested. D- and L-KALA had some in vitro antimalarial effects at 0.025 and 0.05 mg/ml respectively but both forms were haemolytic at 0.1 mg/ml. Potential uses of naturally occurring proteins and their derivatives in the control of insect born infections and topical use of cecropins against leishmaniasis are discussed.

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