THE MECHANISM OF COMPLEMENT FIXATION

1. Complement fixation is obtained in every antigen-antibody reaction involving the presence or formation of a heterogeneous phase (red cells, bacteria, precipitate). 2. The physical constants of fixation (temperature coefficient, velocity, quantitative relationships between the reactants) are those commonly associated with adsorption processes, and are the same in the three types of fixation studied. 3. All the in vitro immune reactions involve an aggregation of immune-serum globulins upon the surface of the antigen. It has been shown that the "fixation" of complement is an adsorption by the aggregates so formed; whether these aggregates are visible as a flocculent precipitate (e.g., sheep serum vs. anti-serum) or concentrated as a surface film on a cellular antigen (sensitized cells; agglutinated bacteria), the reaction is fundamentally the same. 4. As yet, it is unknown whether this adsorption is determined by the physical state of the precipitate, and thus, differs only quantitatively from that by Kaolin, charcoal, normal bacteria, heat-denatured proteins, etc.; or whether the comparatively enormous avidity of these aggregates for complement is due to a specific chemical affinity.     

MULTIPLE LABORATORY EVALUATION OF THE REITER PROTEIN COMPLEMENT FIXATION METHOD

Duplicate Reiter protein complement fixation tests were carried out on different days at the UCLA laboratory on 636 specimens entailing diagnostic problems. Results were in agreement in 94.2 per cent of cases.A comparison of the results obtained with the first RPCF test carried out on 639 diagnostic problem specimens submitted to four Los Angeles laboratories showed disagreement ranging from 10 to 13 per cent.Agreement between RPCF and TPI results in each of the four laboratories ranged from 81.2 to 82.7 per cent.A greater correlation was obtained between RPCF and TPI results than between TPI and STS or RPCF and STS.In the presence of nonreactive RPCF tests, from 5.6 to 7.1 per cent of the specimens tested in each laboratory were reactive to VDRL and TPI tests. Nonreactive VDRL and reactive TPI results ranged from 7.2 to 8.3 per cent of the specimens tested.In the presence of reactive TPI and RPCF results, 5.5 to 6.4 per cent of the specimens tested in each laboratory showed nonreactive VDRL tests.Twenty-nine or 4.6 per cent of 625 specimens tested showed nonreactive VDRL, reactive cardiolipin Kolmer and reactive TPI tests.Of the weakly reactive RPCF, VDRL or cardiolipin Kolmer tests, a higher percentage of the RPCF results gave reactive TPI tests than did either the VDRL or cardiolipin Kolmer procedures.The number of specimens showing discrepant RPCF results upon being retested in the four laboratories ranged from 33 to 68. Reactive TPI tests on those specimens ranged from 30.3 per cent to 54.4 per cent.