[Standardization of the complement fixation test (CFT) in brucellosis. IV. Incubation conditions]

A differentiated time and temperature of incubation were used in the first CFT phase. It was found that the activity of complement fixation (C') decreased in the reaction medium. This was observed in the control system in which at 1 C'H50 hemolysis inhibition increase from 50 to 90% was found after 2 hr at 37 degrees C, after 8 hr at 20 degrees C and after 18 hr at 4 degrees C. Simultaneously, a double increase of the standard serum titre was obtained at 4 and 20 degrees C as compared with that at 37 degrees C. At stable concentration of the antigen and complement the effect of C' fixation was the strongest at 4 degrees C, slightly weaker at 20 degrees C and the weakest at 37 degrees C. The above dependence resulted from a different reaction distribution in the chessboard system at each temperature. In the order from the lowest to the highest antigen dilutions positive reactions were increasing and then subsequently expired at 4, 20 and 37 degrees C, forming an optimal antigen dilution typical for each temperature. In our own standard CFT technique a heat and short C' fixation (37 degrees C for 30 min) were chosen which provided the required reaction sensitivity and permitted to make mass diagnostic examinations. It was also shown that the temperature and time of initial incubation of the antigen-antibody complex had no influence on the effect of C' fixation by this complex. This is supported by joint introduction of the antigen and complement into sera.