Bronchoalveolar lavage T-cell and Ia antigen quantitation by flow cytometry in acute and chronic experimental hypersensitivity pneumonitis

Challenges in the Diagnosis and Management of Fibrotic Hypersensitivity Pneumonitis: A Practical Review of Current Approaches

Recent advances in fibrotic hypersensitivity pneumonitis include improved diagnostic guidance, systematic assessments of immunosuppressive therapy, and the recent availability of antifibrotic therapy (nintedanib) for those with progressive disease. A standardized approach to diagnosis may lead to better inclusion criteria for future therapeutic protocols and delineation of disease or treatment response predictors for real-world management. This review will highlight current diagnostic and treatment challenges and remaining knowledge gaps or areas of uncertainty, with a practical overview of supporting evidence and its clinical implications. Exposure history, serologic testing for antigen sensitivity, bronchoalveolar lavage lymphocytosis, histopathology, and radiologic findings will be covered in the diagnosis section, with immunosuppression, antifibrotic therapy, lung transplantation, and disease prognosis in the treatment and management section.

Elevated levels of bronchoalveolar lavage vitronectin in hypersensitivity pneumonitis

Vitronectin is an adhesive glycoprotein that is present in plasma and the extracellular matrix. Hypersensitivity pneumonitis (HP) is characterized by pulmonary inflammation and damage to the extracellular matrix. Perhaps reflecting this, fibronectin has been found to be elevated in the lower respiratory tract of subjects with HP. Vitronectin, like fibronectin, binds to both extracellular matrix components and cells and may mediate tissue remodeling. Thus, it was investigated whether vitronectin might be increased in bronchoalveolar lavage (BAL) fluid of patients with HP. Vitronectin and, for comparison, fibronectin were measured in BAL fluid from 16 patients with HP and nine healthy control subjects by enzyme-linked immunosorbent assay. Vitronectin was significantly increased in the HP group (658.4 +/- 121.8 ng/ml) compared with the controls (58.4 +/- 11.1 ng/ml, p < 0.001) and was found to be positively correlated with fibronectin. Patients whose last antigenic exposure was 4 or fewer days before the BAL had statistically significantly higher BAL vitronectin and fibronectin than did patients whose last exposure was 5 or more days before the BAL. The serum vitronectin levels did not differ. There was no significant relationship between the lavage fluid vitronectin and fibronectin levels and the BAL cell profile in HP. This study confirms that vitronectin, like fibronectin, is a normal constituent of the lower respiratory tract, and demonstrates that vitronectin is elevated in the lower respiratory tract of patients with HP and may play a role in tissue remodeling and fibrosis in this disease.

Experimental hypersensitivity pneumonitis in the rat: histopathology and T-cell subset compartmentalization

The pathogenesis of hypersensitivity pneumonitis (HP) appears to depend largely on T-cell specificity and interactions with monocytes/macrophages. We studied T-cell subset populations, defined by surface membrane markers with putative functional correlates, present in lung parenchyma and bronchoalveolar spaces of sensitized LEW rats following acute and chronic inhalational challenges with antigen. Our initial hypothesis was that the CD4+ RT6- (TDH) subset, the effector cell of delayed hypersensitivity, would dominate in HP lesions and that CD8+ RT6+ (TS) or CD8+ CD45R+ (TS) subsets, constituting putative suppressor T-cell populations, would dominate in lungs of animals with resolving lesions. We found, however, a heterogeneous population involving all eight of the T-cell subsets that were evaluated. Percentages of the RT6+ phenotype diminished as T cells moved from peripheral blood to lung. Dominant numbers of T cells in acute HP included CD8+ RT6- (TCYT) and CD8+ CD45R- (TCYT) subsets, with putative cytotoxic T-cell activity, in addition to CD4+ RT6- (TDH) cells. We did not demonstrate increases in T suppressor cells as the disease waned.

Uptake of muramyl dipeptide fluorescent congeners by normal rabbit bronchoalveolar lavage cells: a study using flow cytometry

Muramyl dipeptide (MDP) is the minimal adjuvant-active structure of mycobacterial cell walls and is known to activate monocytes/macrophages, but mechanisms involved with uptake and activation of these cells have not been completely defined. Earlier studies addressing uptake of MDP and the question of receptors have utilized radioligands and murine peritoneal macrophages. We used fluorescent congeners of MDP and flow cytometry to explore kinetics and specificity of uptake by bronchoalveolar cells of normal rabbits. Both washed cells and cell suspensions from which the fluorescent congeners were not washed were used, and incubation was carried out primarily at 4 degrees C. Fluorescence microscopy consistently revealed intracellular but no visible membrane fluorescence of alveolar macrophages. Uptake was dose dependent but was not saturable up to concentration limits of fluoresceinated muramyl tripeptide (MTP-FITC) imposed by the system, and was partially inhibited by excess unlabeled MDP, consistent with specific inhibition. Alveolar macrophages, but not lymphocytes, demonstrated specific uptake at 4 degrees C, with rapid on- and off-times. Uptake was enhanced 7-fold at 37 degrees C. Uptake was greater by larger, more granular macrophages than by smaller, less granular macrophages, but no difference in uptake was found when cells of similar size but different densities were compared. The exact mechanism of the rapid uptake at 4 degrees C is uncertain but appears to be competed for by unlabeled MDP.