Quantitative Use of Neufeld Reaction with Special Reference to Titration of Type II Antipneumococcic Horse Sera

The Neufeld reaction has recently been advocated 1 for the diagnosis of the different types of pneumonia directly from the patient's sputum. For this purpose, he advised a monovalent antipneumococcic rabbit serum in order to avoid the non-specific reactions which he obtained with the use of antipneumococcic horse serum. More recently, Cooper and Walter 2 reported this same “swelling” phenomenon when antipneumococcic serum from rabbits was mixed with the homologous pure culture grown in artificial media. This observation led us to examine different samples of antipneumococcic serum by mixing them with specific pure cultures and observing the degree of capsular swelling which resulted. It was found that a serum high in mouse protective units caused much more swelling than a serum low in mouse protective units, also that a serum of high potency could be diluted many times and still give a typical “swelling” reaction. These experiments suggested a possible quantitative application of the Neufeld reaction.

Preliminary work with Type II broth cultures and specific antipneumococcus horse sera showed a definite linear relationship between the number of organisms used and the least amount of antibody required to produce an enlarged capsule. This reaction appeared to be specific. The following method of titration of Type II antibody was then developed:

The culture, either live or formalinized, is diluted with 1% peptone to the required density; the serum is diluted with physiological saline solution. Appropriate amounts of a constant culture dilution and of varying serum dilutions are measured with standard platinum loops, placed on a thin cover-slip, mixed well with a loopful of methylene blue solution, and inverted on a microscope slide. These preparations are incubated 30 minutes in a moist chamber at 37°C., and then examined under a fluorite oil-immersion lens.