Ultrastructural study of the interaction between Acholeplasma laidlawii and antibody

The ultrastructure of agar-grown Acholeplasma laidlawii incubated with specific antiserum or IgM fractions of this antiserum has been investigated by the thin-sectioning technique. Antiserum treatment resulted in the development of giant cells along the colony circumferences and in the coating of normal-size mycoplasmas with a periodically arranged extramembranous layer, consisting of attached immunoglobulins as shown by indirect immunoferritin labelling. The regular structure of the coat was not influenced by changes in temperature or by fixation of the membrane antigens prior to reaction with antibody. Extracellular enveloped viruses were uniformly covered with antibody in these experiments. IgM fractions of antiserum in high concentrations produced a similarly uniform extramembranous layer both on mycoplasmas and viruses. Possible explanations of the difference demonstrated between the regular arrangement of antigenic determinants on A. laidlawii membranes and the previously observed uniform binding of immunoglobulins to Mycoplasma gallisepticum are discussed.