Abstract
GL7 was first described as a late activation antigen in mouse, expressed by pre- and immature B-cells, certain thymocytes, and used since as marker of germinal centers. Later GL7 was also found on some human cell lines and sialic acid residues (Sia) were identified as the critical part of the epitope. Enzymes involved in glycosylation show considerable differences between human and mouse and the specificity of some Sia-binding siglecs also vary between species. Here we investigated GL7 expression and membrane localization in rodent and human immunocytes and lymphoid tissues. Mouse and human cell lines, primary (resting and activated) mouse, rat and human lymphocytes were assayed with flow cytometry and confocal microscopy. Our results show that the GL7 epitope expression pattern is similar in rats and mice. In contrast, human lymphocytes selectively and constitutively express GL7, and its expression level can further increase or decrease upon activation of T and B lymphocytes, respectively. The correlation pattern between GL7 expression and binding of various lectins to the surface immunocytes further confirms that the α2,6-linked Neu5Ac is involved in the GL7 epitope in human, as well. The expressed GL7 epitope (possibly attached to protein or lipid molecules) is highly raft-associated in lymphoid cells. This and its spatio-temporally selective expression suggest possible regulatory or adhesion functions for the GL7 epitope-linked molecule(s) in human.