Determination of autohemolysin formation using the plaque test. Demonstration of autoimmune phenomena following vaccinations and infections.

A simple and sensitive modification of the plaque assay for the evaluation of autohaemolysin-producing cells (APC) in the peripheral blood is described: Very small chambers, (volume less than or equal to 0.03 cc) made out of glass slides (75 X 25 mm), are filled with a diluted (1:7) blood cell suspension. After incubation for 26 hours the haemolytic plaques produced by APC in the thin monolayer of blood cells can be counted under the microcope at a magnification up to 320-fold. The number of APC in guinea pigs immunized with cholera vaccine and in monkeys infected with variola-virus was evaluated by means of this method. Cholera vaccination significantly raised the APC up to 7 days after immunization. In monkeys these cells increased markedly between 4 and 7 days after infection with variola-virus. The increase was less pronounced in animals partially protected by prior vaccination with attenuated vaccinia-virus (MVA-strain) and showing a mild course of variola. Autoimmune mechanisms may exist in apparently normal organisms. They may rise after tissue destruction or cell alteration by infectious or other exogenous agents. The method described might be useful to determine the degree of reactogenicity of bacterial and viral vaccines.