A small molecular weight permeability factor in guinea pig serum: adsorption to antigen-antibody aggregates.

The plasma kinin system is readily activated in vitro by glass and other surface active agents (1, 2). Davies and Lowe (3, 4) showed that in addition to anaphylatoxin a permeability factor, which is not suppressed by antihistamine, is activated when serum is incubated with immune precipitates. They demonstrated the possible role of complement in the generation of this factor (designated Pf/P), but failed to show its relationship to any known chemical mediator. We have presented evidence that guinea pig, rabbit and human serum can be activated by immune aggregates (5), and that such serum contains at least two distinct kinin-forming enzymes in addition to other permeability factors, presumably activators (6, 7). Activation of the kinin system by antigen-antibody complexes is of interest because it may have in vivo significance. We have further investigated the properties of the vascular permeability enhancing material that becomes adsorbed on the immune aggregates.