Effect of actinomyces israelii on human peripheral lymphocytes

Actinomycosis is rare and responds well to antibiotic therapy. The causative organism, Actinomyces israelii which is now considered to be a bacterium, has long been suspected of exerting an immunosuppressive effect. The authors provide further evidence of this in their study of three patients with actinomycosis and four healthy control subjects. Skin reactivity to various standard antigens was depressed in all seven patients. Peripheral lymphocytes from the patients and the control subjects were isolated. A. israelii was added to the cell cultures following challenge with several standard mitogens. Blast transformation in response to phytohemagglutinin was inhibited by A. israelii in all seven subjects, but was preserved in response to concanavalin A and pokeweed mitogen. A. israelii appears capable of inhibiting the subset of human peripheral lymphocytes responsive to phytohemagglutinin stimulation in vitro.