Innate and Adaptive Immunity in Noninfectious Granulomatous Lung Disease

Crystalline silica-induced recruitment and immuno-imbalance of CD4+ tissue resident memory T cells promote silicosis progression

Occupational crystalline silica (CS) particle exposure leads to silicosis. The burden of CS-associated disease remains high, and treatment options are limited due to vague mechanisms. Here we show that pulmonary CD4+ tissue-resident memory T cells (TRM) accumulate in response to CS particles, mediating the pathogenesis of silicosis. The TRM cells are derived from peripheral lymphocyte recruitment and in situ expansion. Specifically, CD69+CD103+ TRM-Tregs depend more on circulating T cell replenishment. CD69 and CD103 can divide the TRM cells into functionally distinct subsets, mirroring the immuno-balance within CD4+ TRM cells. However, targeting CD103+ TRM-Tregs do not mitigate disease phenotype since the TRM subsets exert immunosuppressive but not pro-fibrotic roles. After identifying pathogenic CD69+CD103- subsets, we highlight IL-7 for their maintenance and function, that present a promising avenue for mitigating silicosis. Together, our findings highlight the distinct role of CD4+ TRM cells in mediating CS-induced fibrosis and provide potential therapeutic strategies.

Occupational interstitial lung diseases

Millions of workers are exposed to substances known to cause occupational interstitial lung diseases (ILDs), particularly in developing countries. However, the burden of the disease is likely to be underestimated due to under-recognition, under-reporting or both. The diagnosis of occupational ILD requires a high level of suspicion and a thorough occupational history, as occupational and non-occupational ILDs may be clinically, functionally and radiologically indistinguishable, leading to delayed diagnosis and inappropriate management. A potential occupational aetiology should always be considered in the differential diagnosis of ILD, as removal from the workplace exposure, with or without treatment, is a key therapeutic intervention and may lead to significant improvement. In this article, we provide an overview of the 'traditional' inorganic dust-related ILDs but also address idiopathic pulmonary fibrosis and the immunologically mediated chronic beryllium disease, sarcoidosis and hypersensitivity pneumonitis, with emphasis on the importance of surveillance and prevention for reducing the burden of these conditions. To this end, health-care professionals should be specifically trained about the importance of occupational exposures as a potential cause of ILD.

Sarcoidosis and COVID-19: At the Cross-Road between Immunopathology and Clinical Manifestation

Coronavirus disease 2019 (COVID-19) has been associated with dysregulation of the immune system featuring inappropriate immune responses, exacerbation of inflammatory responses, and multiple organ dysfunction syndrome in patients with severe disease. Sarcoidosis, also known as Besnier-Boeck-Schaumann disease, is an idiopathic granulomatous multisystem disease characterized by dense epithelioid non-necrotizing lesions with varying degrees of lymphocytic inflammation. These two diseases have similar clinical manifestations and may influence each other at multiple levels, eventually affecting their clinical courses and prognosis. Notably, sarcoidosis patients are at high risk of severe COVID-19 pneumonia because of the underlying lung disease and chronic immunosuppressive treatment. In this narrative review, we will discuss interactions between sarcoidosis and COVID-19 in terms of clinical manifestations, treatment, and pathogenesis, including the role of the dysregulated renin-angiotensin system, altered immune responses involving increased cytokine levels and immune system hyperactivation, and cellular death pathways.