Method of titrating antigen for Kahn precipitation test

Abstract

This method aims to overcome variations in antigens employed in the precipitation test for syphilis proposed by the author. Two antigens prepared under identical conditions from two different lots of beef heart, will be likely to show variation in sensitiveness when tested with syphilitic sera. This variation in sensitiveness may be considerably lessened if each antigen is first mixed with salt solution in such proportion as to bring forth its maximum power for producing precipitates with syphilitic sera. Generally speaking, this is accomplished by mixing antigen with minimum amounts of salt solution which will produce opalescent mixtures. Since the mode of adding salt solution to antigen markedly affects the final product, it is obviously important to render all conditions which are likely to affect this titration as constant as possible.

The test tubes used in this titration should not differ from those used in the regular tests. In our experience, tubes of 0.8 to 1 cm. diameter give best results. The set up of the titration is as follows:

Six test tubes receive 0.5 C.C. antigen each. Six similar tubes receive respectively 0.25, 0.5, 0.75, 1, 1.25 and 1.5 C.C. salt solution (0.85 per cent NaCL). The 0.25 c.c. salt solution is now poured into the first antigen tube and the mixture immediately poured back and forth several times. The next antigen tube receives the 0.5 C.C. salt solution in a similar manner. The remaining antigen tubes receive the four increasing amounts of salt solution under similar conditions. It will soon be observed that the first two or three tubes show varying degrees of precipitation, the middle tubes, clouding and the last few tubes, opalescence.