VDRL slide flocculation reaction for syphilis performed on active sera.

The discovery of cardiolipin (Pangborn, 1941a) as the active agent in antigens for sero-reactions for syphilis enabled the production of chemically defined antigens, composed of cardiolipin, purified lecithin (Pangborn, 1941b), and cholesterol. Among the many tube and slide flocculation reactions based on the use of cardiolipin antigens, the Venereal Disease Research Laboratory (VDRL) slide flocculation reaction for syphilis, as described in the Manual of Serologic Tests for Syphilis (1949), has gained a world-wide reputation because of its specificity, sensitivity, and simplicity. All the well established sero-reactions for syphilis except two-the Meinicke tube and slide flocculation reactions (Meinicke, 1917; Meinicke and Holthaus, 1933; Meinicke and Fischer, 1939; Kvittingen, 1948; Schmid and Velaudapillai, 1953) and the Citochol slide flocculation (Schmid and others, 1953) -depend on the use of inactivated sera. Whether this inactivation is performed at 560 C. for 30 min. or at higher temperatures for a shorter time, there is always the need of special equipment, the risk of sera becoming unsuitable for the test, and the risk of loss of time. The postulation of chemically defined and hence uniform batches of antigens is not met by the antigens for the Meinicke and Citochol reactions on active sera, because the former (though Meinicke and Brauer (1953) reported on the use of cardiolipin in its composition) contains balsam of Tolu, which is not a chemically defined substance, instead of cholesterol, and the latter antigen belongs to the group of " crude" heart extract antigens. It seemed therefore worth while experimenting to develop a VDRL test modified for the use of active sera.