Abstract
Alcoholic extracts of beef heart have long been used as antigens in the complement-fixation test for syphilis, but the substances responsible for the serologic activity of such extracts have not been identified. The isolation of a new phospholipid is here reported and evidence is presented that the new substance is the active component of the antigenic extracts. Details of its preparation and chemical properties will be published elsewhere.
The substance was prepared by precipitating alcoholic extracts of beef heart with cadmium chloride, removing lecithin from the precipitate by a recently described method 1 and fractionating the lecithin-free cadmium compounds by precipitation from ether with alcohol and acetone. The purest preparation of the cadmium-free phosphatide contained 4.18% of phosphorus and no nitrogen. It was subjected to repeated purification in the form of the cadmium salt without essential change in chemical or serologic properties and is therefore considered to be a single substance.
An abbreviated complement-fixation technic 2 , 3 based on the quantitative methods of Wadsworth, Maltaner, and Maltaner 4 was employed in testing the serologic activity. High-titered sera from syphilitic patients, diluted in pooled, filtered, normal sera, were used. Control tests with pooled sera from nonsyphilitic persons were negative.
In testing the complement-fixing activity of lipid fractions that have been freed of lecithin, it is necessary to add both lecithin and cholesterol. In the absence of lecithin, such fractions are markedly anticomplementary; in the absence of cholesterol, the purified fractions have not been found to fix complement. The amount of added lecithin was so adjusted that a 1:10 saline dilution of the antigen was not anticomplementary. Alcoholic solutions were made up to contain 0.03% of the test substance, 0.05% of lecithin, and 0.4% of cholesterol, and were diluted with 0.85% sodium chloride by the method used for the routine antigen. 2
Get full access to this article
View all access options for this article.