Quantitative complement fixation

Summary In agreement with the investigations ofKent et al. (4), it was found that blood collected in a modifiedAlsevers solution remains constant for a period of at least 14 days.We also succeeded in proving the same with regard to complement, stored according toRichardson (9) and with regard to amboceptor prepared according to the directions of the New York State Department of Health and stored in an equal volume of glycerol at 4° C.The cheap Eel colorimeter proved very suitable for the standardization of the erythrocyte-suspension and the measurement of the percentage of haemolysis.Success was not obtained by means of the method, used in this investigation, to keep the amount of complement, which under the conditions of the test causes haemolysis of 50% of erythrocytes, so constant, as to make daily complement titration unnecessary.     

Automated complement fixation with low reagent consumption

[This corrects the article on p. 208 in vol. 24.].     

Membrane fluidity and the probability of complement fixation

We develop a mathematical theory of the role of membrane fluidity in the initiation of the IgG mediated complement cascade. The basic assumption is that C1q must be at least doubly bound to activate C1r, but that once C1q is doubly bound, C1r still requires some mean finite time tau to become enzymatically active. If C1q dissociates during this time interval, C1r cannot be activated. We consider the consequences of the simplest model of fluidity--one in which the difference between "fluid phase" lipids and "non-fluid phase" lipids is to allow protein mobility, but not a change in protein conformation. We show that under these conditions fluidity will effect C1r activation only if the rate of formation of multiply bound C1q is limited by diffusion in the membrane. If diffusion in the membrane is not rate-limiting, then, within the framework of this model, fluidity has no effect whatsoever on C1r activation. Thus, an experimental determination that C1q binding is not rate-limited by diffusion in the surface, but that fluidity does effect activation, would suggest a protein conformational change resulting perhaps from altered lipid composition. If diffusion in the surface does rate limit multiple C1q binding, we predict the possibility of an optimum diffusion coefficient for activation. For suitably chosen and reasonable parameter values this optimum will occur in the range (10(-11) less than or equal to D less than or equal to 10(-8) cm2/sec. We predict further, under these circumstances, a precipitous drop in the probability of activation above the optimum. The abrupt switch from a high probability of activation to essentially no probability of activation suggests the possibility of a very sensitive control mechanism exploitable by relatively small changes in membrane lipid composition.