Cyclic regulation of B220 antigen expression in immature B cell lines

Three independent immature B cell lines transformed with temperature-sensitive mutants of Abelson murine leukaemia virus (A-MuLV) persistently expressed B220 antigen detected by both of the anti-B220 antibodies RA3-6B2 and 14.8 during culture at the permissive temperature (35 degrees C). RA3-6B2 recognizes the B220 eptiope and that 14.8 is a CD45RA antibody. However, when the culture temperature was shifted up to the non-permissive temperature (39 degrees C) and the culture was continued for 2-3 weeks, a population of the cells (RA3-6B2-14.8+ cells) that lost RA3-6B2 antigen appeared in all three cell lines. From these populations, RA3-6B2-14.8+ subclones were independently isolated by limiting dilution and the phenotype was stable during culture at the permissive temperature. When the culture temperature of the RA3-6B2-14.8+ subclones was shifted up to the non-permissive temperature and the culture was continued for 2-3 weeks, RA3-6B2 antigen was re-expressed in a subpopulation of the RA3-6B2-14.8+ cells. These results demonstrated cyclic regulation of B220 antigen expression during proliferation and/or differentiation of immature B cell lines.