Question

Discuss the immunopathogenesis of sarcoidosis.

Hint:

The formation of non-caseating granulomas is a hallmark of sarcoidosis, and immune dysregulation primarily involves T-cell activation and cytokine release.

Answer 1

Step 1: Overview of Sarcoidosis.
Sarcoidosis is a multisystem inflammatory disease of unknown etiology, characterized by the formation of non-caseating granulomas, typically in the lungs and lymph nodes, but it can affect any organ system.
Step 2: Immune System Dysregulation.
The immunopathogenesis of sarcoidosis involves an exaggerated T-cell response. When an unknown antigen is encountered, it triggers the activation of CD4+ T-helper cells, leading to the release of pro-inflammatory cytokines such as TNF-α and interleukins (IL-2, IL-12). These cytokines promote granuloma formation.
Step 3: Granuloma Formation.
Granulomas are clusters of macrophages and lymphocytes that form as part of the immune response. In sarcoidosis, these granulomas are non-caseating (i.e., they do not have the necrotic center seen in tuberculosis) and lead to tissue damage and organ dysfunction.
Step 4: Organ Involvement.
The lungs are the most commonly involved organ, with bilateral hilar lymphadenopathy and interstitial lung disease being typical features. Other organs, such as the liver, skin, eyes, and heart, can also be involved in sarcoidosis.