Serum of patients with Behçet's disease induces classical (pro-inflammatory) activation of human macrophages in vitro

Background: Although several immunological abnormalities have been demonstrated in Behçet's disease (BD), the exact mechanism of the inflammatory changes occurring is still unknown. Antigen-presenting cells, such as mononuclear phagocytes, play a major role in the regulation of immune-mediated as well as of non-specific inflammation.

Objective: To investigate the serum activity of patients with BD on antigen and chemokine expression of human macrophages in vitro.

Methods: Serum of 15 patients (8 women, 7 men; mean age 33 +/- 10 years) with BD was incubated with cultured macrophages isolated from peripheral blood of healthy volunteers. Macrophages maintained in patients' serum, fetal calf serum with/without dexamethasone and interleukin (IL)-4 or gamma-interferon were investigated for alternative macrophage-activation-associated CC-chemokine 1 (AMAC-1) and IL-8 mRNA expression by Northern blotting. In addition, cytocentrifuge macrophage preparations were stained with monoclonal antibodies against proteins indicating alternative (anti-inflammatory) macrophage activation, such as MS-1 high-molecular-weight protein (MS-1-HMWP), RM3/1 antigen (CD163) and 25F9, as well as classical (pro-inflammatory) macrophage activation, such as CD11c, class I receptor binding the Fc part of IgG (FcgammaRI: CD64) and class III receptor binding the Fc part of IgG (FcgammaRIII: CD16).

Results: Macrophages treated with patients' serum showed neither AMAC-1 expression nor staining with monoclonal antibodies for MS-1-HMWP, CD163 or 25F9. Concomitant treatment with IL-4/dexamethasone up-regulated significantly the expression of CD163. In contrast, IL-8 mRNA expression and staining for CD11c and CD64 were strongly positive after treatment with serum of patients with BD. CD64 positivity and IL-8 mRNA expression were more prominent in patients with active BD than in patients with inactive disease.

Conclusion: Taken together, our results indicate that serum of patients with BD induces classical (pro-inflammatory) activation of human peripheral blood macrophages in vitro. Our findings suggest that serum factor(s) may be responsible for inflammatory changes in BD.