Immunology of sarcoidosis: old companions, new relationships

The immune determinants of granuloma formation and disease progression in sarcoidosis have not been completely disclosed, and the role of both innate and the adaptive immunity is still under investigation.

M2 macrophage polarization, previously thought to be a specific feature of a progressing and fibrosing disease, has been related to the initial steps of granuloma formation both in animal and in-vitro models. The dysregulation of specific metabolic pathways and autophagy has been associated with disease activity and progression. T cells have been reported to be strongly influenced by a macrophage-driven microenvironment and more dangerous when acquiring hybrid phenotypes (e.g. Th17.1) or even becoming anergic, leading to disease chronicization. Locally released serum amyloid A was suggested to induce a more pro-inflammatory Th17 transcription program. The possible role of in-situ humoral immunity and bone marrow-derived mesenchymal stromal cells has also been highlighted.

Evidence points at microenvironment and cell functional features rather than cell polarization or differentiation as determinants of pathogenesis. In terms of therapeutic implications, future advances will rely on molecular disease profiling, aiming at personalized and combined therapeutic approaches.