Leukocytes: tissue interactions, homeostasis, and host defense. Abstracts of the 41st Annual Meeting of the Society for Leukocyte Biology. November 6-8, 2008. Denver, Colorado, USA.

Abstract

Strongly cationic proteins and polypeptides possessing antibacterial activity in vitro have been isolated from various tissues. These substances may participate in resistance to infection, but evidence has been wanting for their existence in tissues, their delivery to invading bacteria, and their cytotoxicity for bacteria in the distorted microenvironment of infection (Skarnes and Watson, cited in reference i). While investigating natural resistance to infection, Metchnikov found that bacteria were rendered eosinophilic during phagocytosis by guinea pig "microphages." 2 He believed that this was caused by alterations in bacterial permeability. Altered permeability per se, however, does not induce acidophilla in bacteria.' Dubos and MacLeod I found that pneumococci lost basophilia in rabbit tissues. This was attributed to a ribonuclease-like enzyme.8 We found1 that ribonuclease did not render Escherichia coli acidophilic in alkaline solutions. Tomcsik (cited in reference i) observed changes in the refractive properties of Bacillus anthracis capsules exposed to pus and believed this was due to sorption of protamine-like substances. The refractive properties of phagocytized Bacillus megaterium, according to Hirsch,4 were changed in degranulating leukocytes. We found that cationic proteins combined with electronegative bacterial cells in vitro rendered the bacteria cationic (stainable with alkaline solutions of anionic dyes) and killed them.1'5 Escherichia coli,6 Actinomyces israeli,7 and Candida albicans 8 became cationic in vivo. Cationic substances belonging to the host had apparently coated the organisms. Evidence is presented here that bacteria in tissues and polymorphonuclear leukocytes (PMN) can physically combine with cationic proteins in a lethal interaction, and that the cytoplasmic granules of the PMN are a source of the cations.