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We report on a soluble (s) form of CD21 (the C3dg/Epstein-Barr virus receptor, CR2) that is spontaneously released by B and T lymphocytes. Immunoprecipitation with anti-CD21 mAb of culture supernatants of surface and biosynthetically labeled B and T cell lines revealed a single band with an apparent molecular mass of 135 kDa. The molecule exhibited a molecular mass 10 kDa lower than that of membrane CD21. The release of soluble CD21 (sCD21) was time dependent and correlated with a parallel decrease in the expression of the membrane-associated molecule. The protein was also found in culture supernatants of tonsillar B cells and normal human thymocytes. Epitopic analysis using combinations of anti-CD21 monoclonal antibodies (mAb) indicated that sCD21 and membrane CD21 were similarly recognized by mAb directed against short consensus repeats (SCR) 1-2, SCR 4-5 and SCR 9-11. Affinity-purified sCD21 was capable of binding to purified human iC3b and to human recombinant CD23, as assessed by enzyme-linked immunosorbent assay and by using the BIAcore technology. In addition, normal human serum was found to contain a soluble form of CD21 that exhibited a similar molecular mass to that of the molecule shed by B and T cells in culture. The serum form of CD21 was recognized by all anti-CD21 mAb that we tested and showed a high reactivity with mAb directed against SCR 1-2. Our observations suggest that B and T cells shed the extracellular portion of CD21 and release a soluble molecule that retains the ligand-binding properties of CD21, thus having a potential role in immunoregulation.
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
March 1990,
Journal of virology,
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
February 1991,
Journal of immunology (Baltimore, Md. : 1950),
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
December 1989,
The Journal of biological chemistry,
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
July 1984,
Proceedings of the National Academy of Sciences of the United States of America,
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
June 1987,
European journal of immunology,
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
April 1985,
Journal of immunology (Baltimore, Md. : 1950),
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
March 1995,
Journal of immunology (Baltimore, Md. : 1950),
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
December 2007,
The Journal of biological chemistry,
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
June 1995,
European journal of immunology,
V Frémeaux-Bacchi, and
I Bernard, and
F Maillet, and
J C Mani, and
M Fontaine, and
J Y Bonnefoy, and
M D Kazatchkine, and
E Fischer
January 1988,
Journal of immunology (Baltimore, Md. : 1950),
