The claudins are a family of over twenty proteins which are components of tight junctions. Tight junctions are specialized regions of cell-to-cell contact made up of a network of strands to act as a molecular 'gasket' for preventing the leakage of ions, water, etc. between cells. They are abundant in luminal epithelial sheets where they maintain epithelial cell polarity. The claudins constitute a variable component, with specific claudins being associated with specific tissues. The immunoreactivity for anti-claudin 1 is membranous and is found in nearly all carcinomas. The staining is much stronger in the carcinoma cells than in normal tissues. Anti-claudin 1 in a panel of immunostains that includes antibodies against EMA (positive), S-100 (negative), and GLUT1 can be utilized as a robust marker in the diagnosis of perineurioma and neurofibroma. Some studies have shown anti-claudin 1 to be a specific marker for meningiomas. Therefore, anti-claudin 1 with anti-EMA, anti-S-100 protein, anti-CD34, and anti-glial fibrillary acidic protein (GFAP) may be helpful in the differentiation of meningiomas from histologic mimics.
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