Sarcoidosis is a multisystem granulomatous disorder that most often affects the lungs and may cause significant morbidity. Sarcoidosis can manifest as neurological disease, uveitis, blindness, end-stage pulmonary fibrosis, pulmonary hypertension, dysrhythmias, cardiomyopathy, hypercalcemia, and renal failure. Sarcoidosis persists as chronic disease in approximately one-third of those affected. Clinical pitfalls and misconceptions about the course of disease place this population at risk for delayed or inadequate care. While noncaseating granulomas are the histopathological hallmark of sarcoidosis, they also are nonspecific. No pathognomonic diagnostic test exists for sarcoidosis, so the diagnosis remains one of exclusion. While the etiology of sarcoidosis is still unknown, recent insights into its immunopathogenesis have moved investigators closer to finding more effective treatments. Corticosteroids remain the standard of care when treatment is indicated, despite their adverse effect profile. Clinical investigations of novel drugs and biological agents targeting mechanisms involving CD4 type 1 helper T cells may provide more effective, better tolerated therapies.
The HRCT was performed on a black woman in her sixth decade with untreated pulmonary sarcoidosis. It reveals extensive cystic changes involving the upper lobes, bilaterally, as well as severe, interstitial thickening and fibrosis, reflecting stage IV pulmonary sarcoidosis.
In a genetically predisposed host, antigen presentation leads to CD4 T-cell activation, downstream clonal proliferation, and elaboration of type 1 helper T cytokines or chemokines. This promotes cellular accumulation and nidus formation, resulting in granuloma. APC indicates antigen-presenting cell; BTNL2, butyrophilin-like protein 2 gene; CCL, chemokine (C-C motif) ligand; CCR, chemokine (C-C motif) receptor; CXCL, chemokine (C-X-C motif) ligand; CXCR, chemokine (C-X-C motif) receptor; MHC II, major histocompatibility complex II; mKatG, Mycobacterium tuberculosis catalase–peroxidase protein; TCR, T-cell receptor; TGF-β, transforming growth factor β; TLR, toll-like receptor; TNF, tumor necrosis factor.
T-cell activation may occur via the T-cell receptor (TCR), toll-like receptor (TLR), cytokine or chemokine receptors, leading to signal transduction and activation of transcription factors, which promote gene expression controlling T-cell proliferation, differentiation, apoptosis, anergy, and production of proinflammatory cytokines and chemokines. Sites of action of therapies are shown in blue rectangles (see also Table 2). AMP indicates adenosine monophosphate; AP-1, activator protein 1; ATP, adenosine triphosphate; cAMP, adenosine 3′ 5′ cyclic monophosphate; GTP, guanosine triphosphate; ICAM-1, intercellular adhesion molecule 1; LFA-1, lymphocyte function–associated antigen 1; MHC II, major histocompatibility complex II; MAP3K, mitogen-activated protein kinases; NFAT, nuclear factor of activated T cells; NF-κB, nuclear factor κ B; PDE, phosphodiesterase; PDEI, phosphodiesterase inhibitors; PKC, protein kinase C; TNF, tumor necrosis factor; TNFR, TNF receptor.
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