Complement-induced changes in the core structure of sheep erythrocyte membranes: A study by freeze-etch electron microscopy

Abstract

1. 1. Freeze-etch electron microscopy of sheep erythrocyte membranes treated with antibody plus complement reveals increased roughness of the outer-membrane surface but normal morphology and distribution of the membrane intercalar particles. There is a slight decrease in the number of tangential fractures. Occasional ring-shaped particle aggregates occur on external membrane surfaces. 2. 2. Treatment of sheep erythrocyte membranes with lytic doses of lysolecithin or melittin reduces the number of tangential fractures but also does not affet the morphology or distribution of intercalar particles. 3. 3. However, membranes treated with antibody plus complement, lysolecithin or melittin all exhibit a characteristic change after subsequent proteolytic digestion, i.e. extreme aggregation of intercalar particles. Ghosts produced by hypotonic hemolysis, as well as membranes treated with antibody plus inactive complement, do not show any change in particle distribution following protease treatment. Also, membranes treated with antibody plus C6-deficient rabbit serum show no particle aggregation upon protease treatment. 4. 4. The ring-shaped particle aggregates, occasionally seen on the outer-membrane surface following complement action, do not disappear after protease treatment, but become clustered in a manner suggesting very close association with the membrane intercalar particles. 5. 5. We conclude that complement produces a subtle alteration in the structure of the erythrocyte membrane core, which can be mimicked by lysolecithin and the bee venom polypeptide melittin, both membrane-lytic agents.