[The rate constant K37 in complement fixation tests: kinetic studies on the influenza virus-immune complex model...

A kinetic study of the fixation of complement by the influenza immune complex was performed, using an automatic method originally described by Vargues for use in immunobacteriology. The autoanalyser provided curves which could be transformed into a simple equation. The experimental graph of the complement fixation reaction is superposable on a model curve obtained by exponential dilurion of complement. The methematical formula of this exponential complement dilution fits results of complement fixation by the immunecomplex. The rate constant can be estimated from the tangent at the orgin of the curve; it is a function of the nature of the immunesystem, the quantity of immune-complex and the temperature. These results show that the reaction behaves according to the equations of first order kinetics. This law is therefore the same as that described for other immunological systems, such as the seroneutralization of bacteriophage or the fixation of isoagglutinins on red cells. The kinetic study leads to the proposal of the k37 value for the titration of an anti-influenza serum. It is the rate constant of the reaction at 37 degrees C and is independant of the time and temperature of the fixation system as it is of the initial quantity of complement. Increased sensitivity of the reaction does not yield by higher values of k37 but affords greater precision in its calculation. This approach is identical to the one proposed by Adams for the titration of anti-phage sera.