Dissecting inflammatory and chemotactic pathways in Familial Mediterranean Fever
Background: Familial Mediterrean fever (FMF) is a heritable autoinflammatory disease characterized by substantial neutrophil influx at sites of serosal and synovial involvement. Inflammatory attacks are usually prevented by prophylaxis with colchicine, a microtubule inhibitor. Pyrin, the FMF protein, colocalizes with microtubules and may impact leukocyte cytoskeletal functions such as adhesion and migration. We therefore sought to further investigate leukocyte migration in FMF. Methods: Peripheral blood samples were obtained from 25 treated patients, 10 untreated patients, and 16 controls. Subsets of patients were studied in several assays. Chemokines produced from cultured supernatants and from serum samples were evaluated with the Luminex immunoassay. Chemotaxis assays included a transwell system and a live imaging protocol with granulocytes stimulated to various chemoattractants, including MIP-1 alpha, IL-8 and fMLP. Analysis of gene expression sequences with the Affymetrix system was utilized in 8-paired patient samples who underwent colchicine withdrawal. Results: Microarray analysis revealed a “chemotactic signature” induced by colchicine withdrawal with upregulation of major chemotactic genes including CRK, BCL6, ADAMTS 10, and downregulation of genes involving chemokine receptors and cell adhesion molecules such as CCR 7 and CXCR3. At 72 hours off colchicine, monocytes from FMF patients stimulated with LPS produced more TNF-alpha and IL-12p70. Moreover, neutrophil activation was increased, as seen with the downregulation of the L-selectin marker, CD 62L. Patients off colchicine demonstrated significant hyperresponsive cell movement compared with treated patients and controls, although such movement was found to be random (chemokinetic) and less directed (chemotactic) when visualized. FMF patients on colchicine showed elevated serum levels of the chemokines, MIP-1 alpha and beta, as compared to controls. Conclusion: A cascade of intracellular events involving chemokine signaling can impact leukocyte migration in FMF. Current studies are focused on determining the extent to which these effects represent the underlying pathophysiology of FMF, independent of colchicine, by studying colchicine naïve patients.
