Morphological alterations of the lung in the Sickle Cell Trait

Sickle Cell Trait (SCT), besides the increasing evidence of erythrocyte stiffness and the long- term onset of chronic kidney disease in the trait carriers1, is still considered a benign condition. So far, there are still little data regarding the ultrastructural modifications responsible for a pos- sible multi-organ damage in the SCT 2,3. To extend our previous studies on the liver and spleen, we investigated the microanatomical alterations of the lung by conventional light microscopy and transmission electron microscope (TEM) in “healthy” heterozygous subjects. To this aim, we used 13 humanized Townes mice (a chimera expressing falcemic human hemoglobin - HbS): 3 homozygotes (Sickle Cell Disease-SCD), 5 heterozygotes (SCT), and 5 healthy controls; all specimens were analyzed by conventional histological staining, whereas 2 controls and 2 Sickle Cell Trait mice underwent TEM analysis. After surgical removal, part of the tissue samples was paraffin-embedded to perform a light microscopy histopathological analysis. Another part of tissue was rapidly immersion-fixed in glutaraldehyde, reduced into 1x1x3 mm pieces, postfixed in OsO4 , dehydrated, and embedded into epoxy resin. Ultrathin sections of 50-80 nm underwent staining with UranyLess and lead citrate for TEM analysis. The histopathological analysis of SCD lungs showed the classic signs of ischemia. By contrast, in the SCT lungs, low-grade inflammation and minimal capillary congestion were observed. In the semithin sections, the basement membrane of the pulmonary alveoli was often thickened and gave the parenchyma a denser and more irregular appearance compared to con- trols. In SCT mice, the TEM analysis revealed irregular morphology of pulmonary capillaries, their basal lamina showed a thickness three times that of control mice. Moreover, the presence of extremely irregularly shaped erythrocytes was observed. The endothelium also presented numerous extroflexions towards the vascular lumen. The present findings confi rm the presence of chronic vascular damage that could aff ect long-term organ function even in heterozygous mice. While, according to our previous observa- tions, the endothelial alterations are virtually ubiquitous in the liver and spleen, the lung shows the most significant parenchymal alterations. Collectively, these findings contribute novel data to better characterize the morpho-pathological modifications in the SCT mouse model and sug- gest translational usefulness