A Comparative Study of Complement
Authors: Cushing J. E. 
Published: January 2023

Discussion and Summary
The work or the inter-specific reactivations show that, while these occur, they take place only at dilutions that are lower than the intra-specific ones, and one may ask why this should be. The situation is analogous to that observed in comparing the reactions of homologous and related, heterologous, antigens with a given antiserum. Here one also observes that the former reaction always can be obtained at much higher dilutions than the latter. Landsteiner (1936) explains this on the basis of chemical similarity, the more similar the haptens of the antigens being compared, the greater the reaction between heterologous antigen and the antibody. This explanation may also be applied to complement, but not until more is known concerning the kind of linkages involved, and the other related aspects of the probelm have been further studied.
In summarizing Part II, it may be said that the preceding sections have shown that, contrary to former work, some of the components of complement can be successfully interchanged among the carp, frog and guinea pig. The results of such an exchange were extensively studied in the case of the frog and guinea pig, and it was concluded that, here at least, one member of each component had to be present before an action might occur. However, as all combinations in which this was true were not active, a further attempt at analysis was made. While some tentative conclusions were reached, it became apparent that the technics of inactivation were not refined enough to carry the matter further at this time. This circumstance made it unfeasible to attempt a similar analysis of the more complicated combinations between carp and frog and carp and guinea pig, which, however, do show a fair degree cf activity. The general conclusion to be reached is that complement is very similar throughout the vertebrates and is, therefore, a relatively stable character from an evolutionary point of view. Such differences as have occurred do not seem to parallel phylogenetic relation-ships, as will be seen from the discussion of specificity, with the possible exception of that of optimal activity at different temperatures.
In concluding, it should be pointed out that complement appears to have a type of specificity that is often disregarded. This can be determined from the fact that the complement of a given species, or even individual, will react differently with different kinds of antigen-antibody complexes, such differences occurring in an as yet unpredictable fashion as the accompanying table (4) shows. One might suspect that combinátions involving complement and antibody from the same species would be relatively more successful than those involvinginter-specific mixtures, but even this is not secure This is well shown in the human species where it is known that isohemolysis does not occur consistently nor in apparent relation to the amount of antibody present. Of interest in this connection is the report of tteidelberger and Mayer (1942) that human complement is not always fixed by the complex of human antibody and pneumococcus capsular antigen for this raises the possibility that the same unknown factor determines activity in both cases. Also of note is the fact that horse antibody will not react with its own complement to kill H. influenzae although it will do so with human complement (Dingle, Fothergill, and Chandler, 1938).
The present uncertain state of knowledge about the factors involved in a successful complementing reaction has led to various difficulties. Examples of these are to be seen in experiments, for instance, which did not take into account the fact that the complements of some species, such as the sheep and guinea pig, will not hemolyze some kinds of red cells including their own. Such is the case with some attempts to correlate the hemolytic and phagocytic power of complement (e.g. Ecker, Pillemer and Kuehn, 1942) and to compare the complements of various species (e.g. Hegedus and Greiner, 1939, Brown, 1943), as well as to study natural and immune antibodies (Kolmer, 1919). Additional instances could be cited where the failure to account for the possibility of effects due to varying relationships among complement, antigen, and antibody has led to untenable conclusions, but the above should suffice to indicate the complications involved.
Since it is generally accepted that complement acts greatly to enhance phagocytosis under some conditions, practical as well as theoretical importance may be attached to the fact that the activity of complement may vary with the source of TABLE 4The following is a list of examples showing that the activity of a complementing reaction is influenced by the kinds of complement, antigen, and antibody involved, and that variations in any one of these may bring about different results even though the other two are held constant.Active combinations are indicated by an x, inactive by an o, excepting that in cases where differences in degree of activity occur the stronger reaction is shown by a large X in contrast to the weaker.Numbers in last column indicate references at end of tableCOMPLEMENTANTIBODYANTIGENACTIVITYCRITERIONREF.Reactions in which the antigen is variedguinea pighorsepneumococcus capsuleofixation1guinea pighorsepneumococcus proteinxfixation2guinea pighorsepneumococcus C fractionofixation2guinea pighorseH. influenzae capsuleofixation2guinea pighorseH. influenzae proteinxfixation2guinea pighorseB. pestisxfixation3guinea pighorsevarious toxinsofixation4guinea pigrabbitpneumococcus capsulexfixation1guinea pigrabbitpneumococcus proteinxfixation1guinea pigrabbitpneumococcus C fractionofixation1guinea pigrabbitH. influenzae capsulexfixation2guinea pigrabbitH. influenzae proteinxfixation2guinea pigrabbitS. hemolyticus C fractionofixation1guinea pigrabbitS. hemolyticus M proteinxfixation1guinea pigrabbitguinea-pig red cells0hemolysis4guinea pigrabbitsheep red cellsxhemolysis4Reactions in which the antibody is variedguinea pighorsepneumococcus capsuleofixation5guinea pighumanpneumococcus capsuleofixation5guinea pigmousepneumococcus capsuleofixation5guinea pigcatpneumococcus capsuleofixation5guinea pigdogpneumococcus capsuleofixation5guinea piggoatpneumococcus capsuleofixation5guinea pigrabbitpneumococcus capsulexfixation5guinea pigguinea pigpneumococcus capsulexfixation5guinea pigratpneumococcus capsulexfixation5guinea pigsheeppneumococcus capsulexfixation5guinea pigguinea pighuman red cellsxhemolysis6guinea pigrabbithuman red cellsxhemolysis6guinea pigdoghuman red cellsXhemolysis6guinea pigcathuman red cellsXhemolysis6guinea pigchickenhuman red cellsohemolysis6rabbitguinea pighuman red cellsXhemolysis6rabbitrabbithuman red cellsXhemolysis6rabbitdoghuman red cellsxhemolysis6rabbitcathuman red cellsxhemolysis6rabbitchickenhuman red cellsohemolysis6horserabbitox red cellsohemolysis7horsecatox red cellsxhemolysis7horsegoatox red cellsohemolysis7horseduckox red cellsohemolysis7Reactions in which the complement is variedhorserabbitsheep red cellohemolysis8guinea pigrabbitsheep red cellxhemolysis4frograbbitsheep red cellxhemolysis9carprabbitsheep red cellohemolysis10snakerabbitsheep red cellxhemolysis11sheeprabbitsheep red cellohemolysis12humanhumanpneumococcus capsulexfixation13guinea pighumanpneumococcus capsuleofixation5goatgooseox red cellohemolysis14ratgooseox red cellxhemolysis14humanhorsepneumococcus capsuleofixation13guinea pighorsepneumococcus capsuleofixation1guinea pignatural rabbitBrucella suisobactericide15oxnatural rabbitBrucella suisxbactericide15sheepnatural rabbitBrucella suisxbactericide15guinea pigguinea pigHemophilus influenzaexbactericide8rabbitguinea pigHemophilus influenzaexbactericide8humanguinea pigHemophilus influenzaexbactericide8guinea pigrabbitHemophilus influenzaeobactericide8rabbitrabbitHemophilus influenzaexbactericide8humanrabbitHemophilus influenzaexbactericide8Reactions where heterologous combinations of complement and antibody are more active with a given antigen than are homologous oneshorsehorseHemophilus influenzaeobactericide8guinea pighorseHemophilus influenzaeobactericide8humanhorseHemophilus influenzaexbactericide8rabbithorseHemophilus influenzaeobactericide8oxoxox red cellso?hemolysis7rabbitoxox red cellsx?hemolysis7guinea pigrabbit 30-unitssheep red cellsXXhemolysis16rabbitrabbit 30-unitssheep red cellsxhemolysis16humanrabbit 30-unitssheep red cellsXhemolysis16References (see bibliography for complete reference)Goodner and Horsfall, 1936Pittman and Goodner, 1935Kolmer and Tuft, 1941Osborn, 1937Horsfall and Goodner, 1936Noguchi and Bronfenbrenner, 1911Muir, 1911–14Dingle, Fothergill, and Chandler, 1938Reiner and Strilich, 1929Cushing, unpublishedBond and Sherwood, 1939Ecker, Pillemer and Kuehn, 1942Heidelberger and Mayer, 1942Ehrlich and Morgenroth, 1901Shrigley and Irwin, 1937DaCosta, Cruz, and Penna, 1930 antigen and type of antibody involved. This would seem especially so as the phagocytes are held to be the most important natural agents in the destruction of pathogens, which suggests that one of the reasons for failure in cases where serum therapy has been unsuccessful is that antibodies were used that would not react with human complement under the conditions involved. The erratic occurrence of isohemolysis, together with the work of Heidelberger and Mayer, suggests that even the failures with human convalescent serum might sometimes involve unknown individual differences in complementing activity. Similarly, situations where it would be desirable to use the technic of complement fixation, but where fixation has not been demonstrated, as in the toxin-antitoxin reactions (Osborn, 1937), might be re-investigated in terms of new sources of complement and antibody.