Microbicidal cationic proteins in rabbit alveolar macrophages: a potential host defense mechanism

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Abstract
Rabbit alveolar macrophages contain 2 highly cationic microbicidal proteins. These were distinct from histones and did not arise from granulocyte contamination. The macrophage proteins were especially active against Candida albicans and C. parapsilosis. Gram-positive bacteria (Bacillus subtilis, Listeria monocytogenes and Streptococcus faecalis) were also susceptible; Escherichia coli and Salmonella typhimurium appeared more resistant. The proteins may be present in lysosomes, based on their solubilization by dilute acids and their distribution with lysosomal markers on sucrose density gradients. Such microbicidal proteins were not previously demonstrated in any mammalian macrophage. They may play a significant role in the host-defense functions of the rabbit lung.