Activity of rabbit leukocyte peptides against Candida albicans

Six related cysteine-rich, low-molecular-weight peptides were purified from rabbit peritoneal granulocytes and tested in vitro for fungicidal activity against Candida albicans. Two peptides (NP-1 and NP-2) were highly effective, one (NP-3a) was moderately active, and three (NP-3b greater than NP-4 much greater than NP-5) had substantially less potency. There was a general, but imperfect, correlation between the candidacidal potency of each peptide and its net cationic charge. Candidacidal activity by NP-1 was concentration and time dependent and occurred rapidly under optimal low-ionic-strength conditions. It was inhibited by increasing either the ionic strength or Ca2+ concentration of the incubation mixtures, but was relatively unaffected by Mg2+. Candidacidal activity was independent of H+ concentrations between pH 5 and 8, but decreased below pH 5. Candidacidal activity was temperature sensitive and was virtually abolished when NP-1 was incubated with C. albicans at 0 degrees C. Cysteine-rich antimicrobial peptides such as NP-1 and NP-2 may equip leukocytes to deal with infections caused by C. albicans and other fungi that are susceptible to their microbicidal effects.