Oral Immunization of Humans Against Pneumococcus,Determined by the Increased Protective Antibody Content of Serum.

The writer reported 1 that protective antibodies against pneumococcus, type 1, could be found in the sera of rats fed either (1) infected pneumococcus tissue (2) the living organism, or (3) the acid killed organism. Not all sera of rats thus actively immunized were found to contain these transferable antibodies and in those that did, the amounts present neutralized from 10 to 100,000 fatal doses (in 0.20 cc.). Experiments performed on dogs demonstrated similar results. Neither agglutinins nor precipitins could be found in the blood of such orally immunized animals, a statement confirmed recently by Maeji 2 for a rabbit fed type 3 organisms. The absence of agglutinins and precipitins made it appear that a similar condition would possibly be found to exist in humans fed acid killed pneumococci, even if the subjects should be made actively immune by this procedure. Reliance would consequently have to be placed upon the detection of an increased concentration of protective antibodies as a means of determining immunity.

The experiments reported here were done between October, 1928, and October, 1930, and were briefly mentioned elsewhere. 3 The work was interrupted but is now being continued. The results obtained on 14 subjects are reported below.

The sedimented HC1 killed organisms (type 1 throughout) were used directly after centrifugation or after desiccation and were administered generally on a fasting stomach. The quantities fed are listed for each subject.