The effect of the injection of a synthetic platelet-activating factor (PAF-acether) on the fate of IgG aggregates in mice.

The effect of the injection of a synthetic platelet-activating factor (PAF-acether) upon the fate of exogenous immune aggregates was studied in normal mice. When animals received 0.5 μg of PAF-acether following the administration of 5 μg heat-aggregated human IgG (A-IgG), a 50% increase of clearance velocity was observed during the initial 5 min; thereafter, between 15 and 30 min, there was a marked increase in blood levels of immune aggregates which paralleled the increase in plasma volume observed at those times. As regards the effect of the infusion of PAF-acether on the distribution of A-IgG in the organs, hepatic uptake was not affected, kidney uptake was reduced during the first 15 min, and lung and spleen showed only minor variations. When animals were injected with 0.5 μg PAF-acether, skin trapped aggregates showed a 73% increase above control values at 5 min, followed by a fall to control values coincidently with the flood back of the aggregates into the circulation and the increase in blood volume. The injection of lower doses of PAF-acether (0.05 μg) or Diazoxide (1.5 mg) did not induce any change on the skin trapping of aggregates. In conclusion, the powerful action of PAF-acether on vascular permeability allows a reversible deposition of immune aggregates in the skin which is followed by the flood back of this material into the circulation when its pharmacological action subsides. These findings may be of some relevance to the understanding of the dynamic processes involved in the deposition of immune complexes in tissues, especially as regards skin vessels.