Dermatan Sulfate Interacts with Dead Cells and Regulates CD5+ B-Cell Fate

Abstract

CD5 ؉ (B-1a) B cells play pivotal roles in autoimmunity through expression of autoreactive B-cell receptors and production of autoantibodies. The mechanism underlying their positive selection and expansion is currently unknown. This study demonstrates that dermatan sulfate (DS) expands the B-1a cell population and augments the specific antibody response to an antigen when it is in complex with DS. DS displays preferential affinity for apoptotic and dead cells, and DS-stimulated cell cultures produce antibodies to various known autoantigens. The companion article further illustrates that autoantigens can be identified by affinity to DS, suggesting that molecules with affinity to DS have a high propensity to become autoantigens. We thus propose that the association of antigens from dead cells with DS is a possible origin of autoantigens and that autoreactive B-1a cells are positively selected and expanded by DS•autoantigen complexes. This mechanism may also explain the clonal expansion of B-1a cells in certain B-cell malignancies.

Human Proteins with Affinity for Dermatan Sulfate Have the Propensity to Become Autoantigens

“…In the companion article, we demonstrate that DS physically interacts with dead cells and that the resulting DS•autoantigen complexes drive autoreactive B-1a cell responses and autoantibody production in mouse models. 11 Here, we provide further support for our hypothesis with data from human patients and report the identification of approximately 200 human autoantigens with DS affinity.…”

“…Here and in our companion article, 11 we provide experimental support for the hypothesis that complexation of a self-molecule with the glycosaminoglycan DS promotes specific B-1a cell responses and autoantibody production, thus rendering the self-molecule autoantigenic. Using proteome fractionation as a physicochemical selection mechanism for interrogating affinity to DS, we identified 246 distinct proteins (eluting at Ն0.4 mol/L NaCl; Tables 1 and 2; see also Supplemental Appendix and references therein at http://ajp.amjpathol.org), of which at least 147 (59.8%) are previously well-known autoantigens or closely related to known autoantigens.…”

“…11 This also holds for human WIL2-NS cells ( Figure 3). As shown by electron microscopy, DS preferentially associates with dead cells or cell debris, supporting the notion that dead cells serve as a source of autoantigens.…”

“…Cells were fixed with 4% paraformaldehyde at 25°C for 30 minutes and processed as described. 11 Sections of cells were stained with goat anti-biotin conjugated to 20-nm gold particles and examined with a JEOL 1200EX transmission electron microscope (JEOLO USA, Peabody, MA).…”

“…11 Nunc MaxiSorp 96-well plates were coated with 0.1 mg/mL DS or 2.5 g/mL goat anti-human F(ab=) 2 at 4°C overnight. Wells were blocked with 1% bovine serum albumin at 25°C for 1 hour.…”