Xenograft rejection in marine sponges. Isolation and purification of an inhibitory aggregation factor from Geodia cydonium.

In sponges there exists a graft rejection mechanism in which an inhibitory aggregation factor is involved. The inhibitory aggregation factor has been isolated from a culture medium containing dissociated cells of the sponge Geodia cydonium. Using ion-exchange and gel fractionation the factor was purified and shown to be electrophoretically pure. The factor has a molecular weight of 27000 and was characterized as a glycoprotein. The activity of the inhibitory aggregation factor was not affected by heat treatment, but treatment with trichloroacetic acid resulted in the irreversible loss of activity. The inhibitory aggregation factor affects the aggregation-factor-mediated reaggregation of dissociated sponge cells by extension of the lag phase preceding the aggregation process; the endpoint of the reaggregation process is not changed. The inhibitory aggregation factor competes with the aggregation receptor for the binding site on the aggregation factor. The inhibitory aggregation factor is not synthesized if homologous aggregation factor is added to the dissociated cells. The results indicate that the inhibitory aggregation factor is synthesized in xenografts of the system Geodia cydonium--Geodia rovinjensis after a grafting period of at least 3 days. Following the synthesis of the factor, the concentration of the extractable aggregation factor decreases.