Neutral glycosphingolipids of the globo-series characterize activation stages corresponding to germinal center B cells.

The neutral glycosphingolipid (GSL) globotriaosylceramide (Gb3) of the globo-series was recently defined as the CD77 antigen. This B cell-associated antigen is characterized by its specific expression on germinal center B cells. In order to study the potential relation of the CD77 antigen and other GSLs to B cell activation we have performed a comprehensive analysis of the synthesis and expression of neutral GSL in tonsillar B lymphocytes. Monoglycosylceramide (GL1) and lactosylceramide (LacCer) comprised the largest portion of GSL in tonsillar B lymphocytes as detected by HPLC analysis. GSLs of the globo-series Gb3 and globotetraosylceramide (Gb4), were found in smaller amounts. Since other GSLs, like gangliotriaosylceramide (Gg3) and gangliotetraosylceramide (Gg4), could only be detected using highly sensitive antibody reactions, we assume that these GSLs occur in B cells only in minor amounts. When tonsillar B cells were density fractionated on Percoll, the light density cells, which correspond to activated cells, contained and expressed more of both globo-GSLs than cells in the higher density fraction. When the dense fraction of tonsillar B cells was activated in vitro by anti-mu/BCGF, synthesis of GL1, LacCer, Gb3, and Gb4 was biphasic, with maxima at 12 and 84 h. Surface expression of the CD77 antigen on the denser cells was strongly induced by anti-mu/BCGF during the first 24 h of cultivation followed by a rapid decline thereafter, mimicking synthesis. PMA treatment of this cell fraction caused an even stronger expression of the CD77 antigen, which lasted over 48 h of cultivation.(ABSTRACT TRUNCATED AT 250 WORDS)