Clearance of antibodies from rat sarcoma cell surfaces. Rate of clearance of alloantibodies depends on antibody isotype.

The influence of antibody isotype on the lifetime of complexes involving cell surface antigens of the rat fibrosarcoma HSN.TC has been investigated using direct binding and competitive RIAs to monitor the antibodies. Alloantibodies of the IgG class that had bound to the cells during a 1-hr exposure to antiserum were cleared subsequently from the cell surface by an active process involving two distinct phases. Between 30 and 70% of these antibodies were lost in the first 10 hr but the antibodies remaining were cleared more slowly with half-lives ranging from 20 to 40 hr. Antibodies of the IgM class, however, and those that could bind Clq and initiate the complement cascade were cleared rapidly with half-lives of less than 3 hr. Analysis of total cell-associated immunoglobulin showed that the disappearance from the cell surface was not a consequence of intracellular accumulation of antibody but was caused by the release of the antibody in a degraded form. The surface expression of the majority of the alloantigens involved was not affected by continuous exposure to antibody although modulation of a subpopulation of antigens could not be excluded. These results suggest that the clearance of alloantibodies involved their internalization and degradation and that antibodies capable of forming multimeric complexes were cleared rapidly. Some of the IgG-containing complexes, however, exhibited extended lifetimes at the cell surface, suggesting that either they were not internalized or they were recycled between the cell interior and the plasma membrane.