Pneumocyte injury and ubiquitin-positive pneumocytes in interstitial lung diseases

Exploring the Immune Response against RSV and SARS-CoV-2 Infection in Children

Viral respiratory tract infections are a significant public health concern, particularly in children. RSV is a prominent cause of lower respiratory tract infections among infants, whereas SARS-CoV-2 has caused a global pandemic with lower overall severity in children than in adults. In this review, we aimed to compare the innate and adaptive immune responses induced by RSV and SARS-CoV-2 to better understand differences in the pathogenesis of infection. Some studies have demonstrated that children present a more robust immune response against SARS-CoV-2 than adults; however, this response is dissimilar to that of RSV. Each virus has a distinctive mechanism to escape the immune response. Understanding the mechanisms underlying these differences is crucial for developing effective treatments and improving the management of pediatric respiratory infections.

Expression of the Autoantigen Topoisomerase-1 is Enriched in the Lung Tissues of Patients With Autoimmune Interstitial Lung Disease: A Case Control Study

BACKGROUND

Among the autoimmune rheumatic diseases, it is striking that autoantibodies targeting ubiquitously expressed proteins (eg, topoisomerase-1) associate with specific clinical complications (eg, interstitial lung disease [ILD]). It has been proposed that enriched antigen expression in inflamed target tissue may play a role in focusing the autoimmune response. We sought to determine whether topoisomerase-1 expression is enriched in lungs from patients with autoimmune/inflammatory diseases relative to normal lung.

METHODS

We used a 99-core lung tissue microarray (TMA) containing lung tissue from 40 patients with autoimmune inflammatory ILD (cases) and 46 control subjects with normal lungs. We stained the TMA with antibodies to compare topoisomerase-1 and CD8 expression between patients and control subjects and evaluated whether expression is enriched in specific cell types. Staining was analyzed, and statistical comparisons were performed.

RESULTS

Cases were more likely to have global topoisomerase-1 expression (53% vs 21%; P = 0.003), specifically in pneumocytes (47% vs 16%; P = 0.003) and stromal/immune cells (32% vs 5%; P = 0.002) compared with control subjects. CD8 cell density (223 cells/mm² vs 102 cells/mm² ; P = 0.018) was significantly higher in topoisomerase-1-positive lung tissues compared with topoisomerase-1-negative lung tissues. Interestingly, topoisomerase-1 expression was significantly more common in scleroderma compared with normal lung (67% vs 21%; P = 0.036) and was present more frequently in pneumocytes in these patients (67% vs 16%; P = 0.018).

CONCLUSIONS

Pulmonary expression of topoisomerase-1 is increased in the setting of autoimmune ILD relative to normal lung, specifically in pneumocytes. This may contribute to the amplification of pulmonary disease in patients with scleroderma with a loss of tolerance to topoisomerase-1.

Accumulation of Ubiquitin and Sequestosome-1 Implicate Protein Damage in Diacetyl-Induced Cytotoxicity

Inhaled diacetyl vapors are associated with flavorings-related lung disease, a potentially fatal airway disease. The reactive α-dicarbonyl group in diacetyl causes protein damage in vitro. Dicarbonyl/l-xylulose reductase (DCXR) metabolizes diacetyl into acetoin, which lacks this α-dicarbonyl group. To investigate the hypothesis that flavorings-related lung disease is caused by in vivo protein damage, we correlated diacetyl-induced airway damage in mice with immunofluorescence for markers of protein turnover and autophagy. Western immunoblots identified shifts in ubiquitin pools. Diacetyl inhalation caused dose-dependent increases in bronchial epithelial cells with puncta of both total ubiquitin and K63-ubiquitin, central mediators of protein turnover. This response was greater in Dcxr-knockout mice than in wild-type controls inhaling 200 ppm diacetyl, further implicating the α-dicarbonyl group in protein damage. Western immunoblots demonstrated decreased free ubiquitin in airway-enriched fractions. Transmission electron microscopy and colocalization of ubiquitin-positive puncta with lysosomal-associated membrane proteins 1 and 2 and with the multifunctional scaffolding protein sequestosome-1 (SQSTM1/p62) confirmed autophagy. Surprisingly, immunoreactive SQSTM1 also accumulated in the olfactory bulb of the brain. Olfactory bulb SQSTM1 often congregated in activated microglial cells that also contained olfactory marker protein, indicating neuronophagia within the olfactory bulb. This suggests the possibility that SQSTM1 or damaged proteins may be transported from the nose to the brain. Together, these findings strongly implicate widespread protein damage in the etiology of flavorings-related lung disease.