Antibodies to CD20 and MHC class II antigen bound to B-lymphoma cells accumulate in shed cytoplasmic fragments

Antibodies (Abs) to CD20 and MHC class II antigen were found to exhibit a novel processing pathway after binding to the surface of RL B-lymphoma cells. The Abs were ‘excreted’ as a part of large cytoplasmic fragments. These fragments formed at cell–cell junctions, but gentle dispersal of the cells, to form a single-cell suspension of high viability, caused the release of most of the fragments. This process also occurred in Raji cells and in three other B-lymphoma cell lines (of seven tested). Six B-lymphoblastoid cell lines tested did not form these objects. Once they were recognised, the fragments could be identified in cell preparations by phase contrast microscopy or after staining with Wright's stain. They were induced by the binding of certain Abs, but not by most Abs bound to the cell surface. The mode of formation, detailed morphology and function of these cytoplasmic fragments remain to be determined. They are similar in many respects to the lymphoglandular bodies that have been described by pathologists for many years, which are characteristic of B-cell lymphoma, but which have not previously been described in cell lines. This type of Ab processing, if it occurs in patients, will have an impact on the therapeutic use of these Abs.