Note on the Mechanism of Specific Agglutination

Abstract

One consequence of the “lattice”-theory of serological reactions∗ is that if 2 or more independent antigens and their respective antibodies are all mixed together, each system should aggregate independently. By using microscopically visible and distinguishable particulate antigens† (e.g., bacteria and/or erythrocytes) this prediction has been recently tested. 1 2 3 4 5 In many cases the individual aggregates were chiefly or entirely composed of only one of the 2 kinds of antigenic particles, but the observation has also been made, which seems difficult to account for on the basis of the lattice-theory, that in some cases the aggregates are heterogeneous, i.e., contain both kinds of antigenic particles. Mixed aggregation is also indirectly indicated by the results of experiments with precipitins, 3 , 4 where the rate of flocculation in mixed systems is definitely accelerated in the zones of equivalence and excessive antibody where the increased cohesive effect due to combined antibody (plus electrolyte and lipin) could be expected to exert a dominant influence.

It should be pointed out that the occurrence of homogeneous aggregates, though compatible with the lattice-theory, does not actually prove that the lattice-mechanism was in fact operative in building up the aggregates. Antibody-molecules are invisible and the postulated alternation of antibody and antigen-particles cannot actually be observed. The existing evidence would support equally any hypothesis calling for a certain amount of specificity in the second stage. Also the supposed analogy with crystal-formation is imperfect because for the lattice-structure of some crystals it is not required that different kinds of atoms be alternately interposed.

The essential difference between the lattice-hypothesis and the older concept concerns the mechanism by which the primary compounds of antigen and antibody combine to form aggregates (agglutinated cells or particles of precipitate).