Demonstration of CXCL13 protein and CXCL13 mRNA in skin biopsy samples. (A) Hematoxylin and eosin staining of skin sample from a patient with cryoglobulinemic active vasculitis. Magnification, 10×/0.25. (B) CXCL13 protein immunofluorescence staining in skin biopsy showing feature of active vasculitis. CXCL13- specific signal appears as linear green deposits along collagen bundles. Magnification, 10×/0.25. (C) Complete absence of CXCL13 immunoreactant in skin tissue of an MC patient without active phase of vasculitis. Magnification, 10×/0.25. (D) Positive control staining in human tonsil. Magnification, 20×/0.40. (E) RT-PCR analysis of CXCL13 mRNA extracted from MC patients with and without active cryoglobulinemic vasculitis.