The CD40 pathway is a key mediator of inflammation and autoimmunity. We investigated cell adhesion molecule (CAM) up-regulation and chemokine production by CD40-positive human intestinal fibroblasts (HIF) and microvascular endothelial cells (HIMEC) induced by CD40 ligand (CD40L)-positive T cells and soluble CD40L and their effect on T-cell adhesion and transmigration.

Expression of CD40, CD40L, and CAM was assessed by immunohistochemistry, confocal microscopy and flow cytometric analysis, and chemokine production using enzyme-linked immunosorbent assay. Calcein-labeled T cells were used to assay HIF adhesion and Transwell HIMEC transmigration.

Ligation of CD40-positive HIF and HIMEC by CD40L-positive T cells or soluble CD40L induced up-regulation of CAM expression as well as interleukin-8 and RANTES production. The specificity of these responses was shown by inhibition with a CD40L blocking antibody and by CD40 signaling-dependent p38 mitogen-activated protein kinase phosphorylation. On CD40 ligation, HIF increased their T-cell binding capacity and generated chemoattractants able to induce T-cell migration through HIMEC monolayers.

Activation of the CD40/CD40L system in the gut mucosa may trigger a self-sustaining loop of immune-nonimmune cell interactions leading to an antigen-independent influx of T cells that contributes to chronic inflammation.