Functional expression of the alpha 2-macroglobulin receptor CD91 in salivary gland epithelial cells.

CD91 molecule is a multifunctional receptor of alpha 2-macroglobulin, heat-shock proteins and calreticulin. CD91 has been implicated in cross-presentation of peptides chaperoned by these proteins to MHC molecules, thus eliciting antigen-specific immune responses. Hence, CD91 is considered as a major regulator of innate and acquired immune responses. Herein, we show that CD91 molecules are expressed by human salivary gland epithelial cells (SGEC), as indicated by immunohistochemical studies in minor salivary gland biopsy tissues (n = 21) as well as by the analyses of human long-term cultured non-neoplastic SGEC lines (n = 11) and the neoplastic HSG cell line. In these cell lines CD91 expression was evaluated by RT-PCR, flow cytometry and confocal microscopy. Standard internalization assays revealed that HSG and SGECs are capable to bind and internalize the CD91 ligand alpha 2-macroglobulin. This internalization is specific, as attested by inhibition studies using unlabeled alpha 2-macroglobulin and a blocking antibody against human CD91 receptor. Conclusively, our findings indicate that SGEC functionally express CD91 receptor, suggesting that this pathway might be involved in the presentation of exogenous antigens in SGEC.

Anti-CD40 antibodies in antiphospholipid syndrome and systemic lupus erythematosus.

Anti-beta2glycoprotein I (anti-beta2GPI) antibodies constitute the main autoantibody specificity in the sera of patients with antiphospholipid syndrome (APS). There is evidence that anti-beta2GPI antibodies induce the precoagulant activity of the endothelium by cross-linking the beta2 glycoprotein I (beta2GPI) on the cell surface. Since beta2GPI lacks intracellular domains, homology with other molecules such as CD40 that could initiate signaling, was extensively searched. A 86% homology between the amino acid position 239-245 of the CD40 and 7-13 of the beta2glycoprotein was found. The CD40 peptide corresponding to amino acids 239-245 of the CD40 molecule was synthesized and coupled to a multiple antigenic peptide carrier. Antibodies to CD40 peptide were found in 61.5% APS patients (n = 39), in 72.7% of systemic lupus erythematosus (SLE) positive for anti-beta2GPI antibodies (n = 11) and 31.6% of SLE negative for anti-beta2GPI antibodies (n = 19), but not in rheumatoid arthritis patients (n = 28) or controls (n = 36). Antibodies to CD40 peptide were associated with arterial thrombosis and/or brain microinfarcts. Affinity purified anti-CD40 peptide antibodies as well as affinity purified anti-beta2GPI antibodies recognized both, the beta2GPI and the CD40 peptide. The specificity of this recognition was confirmed with homologous and heterologous inhibition experiments. Confocal microscopy experiments demonstrated this cross-recognition of CD40 and beta2GPI molecules, by the purified anti-CD40 peptide antibodies, at the protein level. Thus, antibodies reacting with the beta2GPI can react and potentially activate different cells which express CD40 molecules at their surface.