The conglutination phenomenon. IV. An experimental investigation of the factors determining the adsorption of complement by an antigne-antiserum mixture

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Abstract
1. Salmonella antisera from a number of animals, including man, have been examined by conglutinating complement-absorption and haemolytic complement-fixation tests for the presence of anitbodies. Both a soluble antigen and a particulate antigen of washed suspended orgainsms have been used. The behavior of the antisera was comparable with that previously recorded with the mallein antimallein system, in so far as the reactions obtained with the different complements followed the same general pattern.2. Two factors were found to explain the failure of certain antisera, in conjunction with the antigen, to adsorb certain complements. On the one hand, a few antibodies themselves appeared incapable of fixing a particular complement. On the other hand, although some antisera failed to fix specific complements, their antibodies, isolated from the serum, were able to fix the complements concerned. In these cases it appeared that the heated serum contained a non-specific factor that prevented the adsorption of the complements.3. The existence of such non-specific factors in certain heat-inactivated sera is illustrated in Figs. 11–14. An examination of the mechanism involved does not appear to implicate the procomplementary effect of sera, although this effect in itself is a complex problem requiring further elucidation. The few experiments carried out indicate that the factor in the inactivated serum does not come into play and inhibit the adsorption of complement by an antigen-antibody complex without the initial intervention of some component of complement. Only after this has occurred is the inhibitory factor able to block any further complement adsorption.4. We have discussed the implications of these experiments and their possible relationships to the complementoid phenomena described by previous workers.