Background/Purpose:

OX40/OX40L interaction is a pivotal costimulatory pathway involved in multiple autoimmune diseases. It provides a key signal for T-cell proliferation and differentiation in effector and memory subsets. Polymorphisms of OX40L are involved in the genetic predisposition to primary Sjögren’s syndrome (pSS). Since SGECs express other costimulatory molecules such as CD80, CD86 or ICOSL, we investigated the expression of OX40L by salivary gland epithelial cells (SGECs) and the expression of OX40 by T cells cocultured with SGECs.

Methods:

Primary culture of salivary epithelial cells was derived from minor salivary gland biopsies isolated from patients with SS or control subjects (complaining from dry symptoms without any feature of autoimmunity). Expression of OX40L by SGEC was measured using qPCR and immunohistochemistry. Naïve CD4⁺ T cells were activated by anti-CD2, anti-CD3 and anti-CD28 and cultured alone or with SGECs. T-cell expression of OX40 was analyzed using flow cytometry. T-cell proliferation and survival were assessed by CFSE dilution and propidium iodide (PI)/DiOC6 staining, respectively. Levels of IFN-γ, IL-2, IL-4 and IL-6 were assessed in culture supernatants using ELISA.

Results:

SGECs isolated from pSS patients (n=4) or controls (n=4) expressed OX40L mRNA and protein. Coculture of T cells with SGECs from patients with pSS (n= 7) significantly increased the expression of OX40 by CD4+T cells (67.3% ± 9.2) compared to T cells cultured alone (33.9% ± 6.9,  p= 0,02). A similar induction of OX40 expression was observed in coculture of T cells  with SGECs from  controls.

In addition, SGECs isolated from pSS patients promoted T cell survival and proliferation : 82% vs 22% living T cells (PI negative DiOC6 positive) were detected when cultured with SGEC, compared to cultured alone. IFN-γ and IL-2, markers of T-cell proliferation and activation, were detected in the supernatant of cocultures  (8.3 ± 0,2ng/ml for IFN-γ and 4.8 ± 0,4 ng/ml for IL-2) but not in the supernatant of SGEC or of T cells cultured alone. IL-6 was also increased in the supernatants of cocultures (2,7 ± 0,6 ng/ml, compared to SGECs isolated from pSS cultured alone (1,2 ± 0,7 ng/ml), or T cells cultured alone (0 ng/ml). The induction of T-cell expression of OX40 was not altered when the coculture of T cells and SGECs was performed using a transwell or not (n=3), which demonstrates that this OX40 induction depends on cytokine(s) and not of cell-cell contacts. 

Conclusion:

SGECs are capable to induce a dramatic increase of OX40 expression, and promote T-cell survival, proliferation and activation. This crosstalk between epithelial and T cells might also result in subsequent B-cell activation as shown by the increase of IL-6 in coculture supernatants. Further analyses are ongoing to determine the mechanisms involved in the induction of OX40 and consequences on T-cell polarization. These results demonstrate a new mechanism by which salivary gland epithelial cells play a pathogenic role in this autoimmune epithelitis. These results also suggest that OX40/OX40L might represent relevant therapeutic targets in pSS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-new-pathogenic-role-of-salivary-gland-epithelial-cells-in-the-costimulation-of-t-lymphocytes-in-primary-sjogrens-syndrome-0x40-ligand-expression-t-cell-induction-of-ox40-and-promotion-of/