Emperipolesis and cell death in NOD2-related Blau Syndrome and Crohn’s disease

Abstract

Background: Blau Syndrome (BS), a rare autoinflammatory disease characterized by non-caseating granulomas, is caused by gain-of-function mutations in NOD2. Crohn's disease (CD) is associated with intestinal granulomas, and SNPs in NOD2. Emperipolesis, the 'inside round about wandering' of lymphocytes within other cells is a typical feature of Rosai- Dorfman disease, and seen occasionally in malignancies. Cell survival and cell death are possible outcomes for both the engulfed and engulfing cells. Aim: To investigate emperipolesis and cell death in BS and CD granulomas. Methods: Morphological and immunohistochemical study of granulomas was undertaken in 8 BS and 7 pediatric CD biopsies, using H&E and immunohistochemistry for leukocyte markers (CD68, CD4, CD8, CD20), cytokines (IFN(gamma), IL6, IL10, IL17, TGF(beta), TNF(alpha)) and death-proteins (Bcl2, Fas, FasL, activated caspase 3). Results: All BS biopsies showed polycyclic granulomas with large lymphocytic coronas and extensive emperipolesis of lymphocytes within multinucleated giant cells (MGCs). This was associated with macrovesicular/ microvesicular degeneration of lymphocytes inside MGCs (Fig1a), and MGC death (Fig1b). Emperipolesis selectively involved CD4+ T cells. In addition, vesicles and degenerative remnants inside MGCs stained strongly for IL-6 and IL-17. A moderate expression of Bcl2 was present, Fas and FasL expression were seen in emperipoletic lymphocytes and MGCs but caspase 3 was virtually absent. In contrast, CD biopsies demonstrated simple isolated granulomas with subtle lymphocytic coronas; emperipolesis was sporadically found in a few biopsies, and was associated with crystalline inclusions, but not with MGC death. Conclusion: Emperipolesis of CD4+lymphocytes is an important feature of BS and is associated with MGC death. NOD2 mutations causing NF-(kappa)B hyperactivation and influencing autophagy pathways may be involved. In CD with NOD2-SNPs, emperipolesis is exceptional and crystalline inclusions are present. (Figure Presented).