A closer look into the GL7 antigen: its spatio-temporally selective differential expression and localization in lymphoid cells and organs in human.

The GL7 epitope was originally described as part of a late lymphocyte activation antigen expressed in mouse and widely used since then as a marker of germinal center. Here we report on its differential expression by rat and human immune cells and lymphoid organs. Expression pattern of the GL7 epitope in rats is similar to that described earlier in mice, namely that GL7 antigen appears only on lymphocytes after 48h activation. In humans lymphocytes, but not the differentiated cells of myeloid origin, express this epitope. The GL7 epitope is up-regulated upon in vitro activation of primary T cells, while a slightly decreased expression is found on B lymphocytes. Fluorescent immunohistochemistry shows discrete location of GL7(hi) cells in human tonsil. GL7 antibody intensely stains CD19(+), IgD(+), IgM(low) B lymphocytes found at the margin of B cell follicles. The GL7 epitope is constitutively and highly raft-associated in human lymphoid cells. Strong neuraminidase- and partial papain-sensitivity of the GL7 epitope on human lymphocytes indicates a sialic acid-containing epitope linked either to one (or more) membrane protein(s) or to lipids. The lymphocyte-restricted GL7 epitope expression and the activation-dependent bi-directional change in the amount of the epitope suggest a functional role for GL7 epitope linked to carbohydrate-based immunoregulation.