Immunoelectronmicroscopic study on the transport of secretory IgA in the lower respiratory tract and alveoli

Serum IgA augments adhesiveness of cultured lung microvascular endothelial cells and suppresses angiogenesis

Immunoglobulin A (IgA) is important in local immunity and is also abundant in the blood. This study aimed to evaluate the effects of serum IgA on cultured lung microvascular endothelial cells (HMVEC-Ls), which are involved in the pathogenesis of inflammatory lung diseases. Serum IgA induced adhesion molecules and inflammatory cytokine production from HMVEC-Ls, and enhanced adhesion of peripheral blood mononuclear cells to HMVEC-Ls. In contrast, migration, proliferation, and tube formation of HMVEC-Ls were significantly suppressed by serum IgA. Experiments with siRNAs and western blotting revealed that two known IgA receptors, β1,4-galactosyltransferase 1 (b4GALT1) and asialoglycoprotein receptor 1 (ASGR1), and mitogen-activated protein kinase and nuclear factor-kappa B pathways were partly involved in serum IgA-induced cytokine production by HMVEC-Ls. Collectively, serum IgA enhanced cytokine production and adhesiveness of HMVEC-L, with b4GALT1 and ASGR1 partially being involved, and suppressed angiogenesis. Thus, serum IgA may be targeted to treat inflammatory lung diseases.

Know your enemy or find your friend?-Induction of IgA at mucosal surfaces

Most antibodies produced in the body are of the IgA class. The dominant cell population producing them are plasma cells within the lamina propria of the gastrointestinal tract, but many IgA-producing cells are also found in the airways, within mammary tissues, the urogenital tract and inside the bone marrow. Most IgA antibodies are transported into the lumen by epithelial cells as part of the mucosal secretions, but they are also present in serum and other body fluids. A large part of the commensal microbiota in the gut is covered with IgA antibodies, and it has been demonstrated that this plays a role in maintaining a healthy balance between the host and the bacteria. However, IgA antibodies also play important roles in neutralizing pathogens in the gastrointestinal tract and the upper airways. The distinction between the two roles of IgA - protective and balance-maintaining - not only has implications on function but also on how the production is regulated. Here, we discuss these issues with a special focus on gut and airways.

Secretory IgA from submucosal glands does not compensate for its airway surface deficiency in chronic obstructive pulmonary disease

Secretory immunoglobulin A (SIgA) reaches the airway lumen by local transcytosis across airway epithelial cells or with tracheobronchial submucosal gland secretions. In chronic obstructive pulmonary disease (COPD), deficiency of SIgA on the airway surface has been reported. However, reduction of SIgA levels in sputum and bronchoalveolar lavage (BAL) fluid has not been consistently observed. To explain this discrepancy, we analyzed BAL fluid and lung tissue from patients with COPD and control subjects. Immunohistochemical analysis of large and small airways of COPD patients showed that MUC5AC is the predominant mucin expressed by airway epithelial cells, whereas MUC5B is expressed in submucosal glands of large airways. Dual immunostaining with anti-IgA and anti-MUC5B antibodies showed reduction of IgA on the airway surface as well as accumulation of IgA within MUC5B-positive luminal mucus plugs, suggesting that luminal SIgA originates from submucosal glands in COPD patients. We found that the concentration of SIgA in BAL is inversely correlated with forced expiratory volume in 1 s (FEV₁) in COPD, but that the ratio of SIgA/MUC5B is a better predictor of FEV₁, particularly in patients with moderate COPD. Together, these findings suggest that SIgA production by submucosal glands, which are expanded in COPD, is insufficient to compensate for reduced SIgA transcytosis by airway epithelial cells. Localized SIgA deficiency on the surface of small airways is associated with COPD progression and represents a potential new therapeutic target in COPD.

Freshly isolated rat alveolar type I cells, type II cells, and cultured type II cells have distinct molecular phenotypes

We used microarray analysis with Affymetrix rat chips to determine gene expression profiles of freshly isolated rat type I (TI) and TII cells and cultured TII cells. Our goals were 1) to describe molecular phenotypic "fingerprints" of TI and TII cells, 2) to gain insight into possible functional differences between the two cell types through differentially expressed genes, 3) to identify genes that might indicate potential functions of TI cells, since so little is known about this cell type, and 4) to ascertain the similarities and differences in gene expression between cultured TII cells and freshly isolated TI cells. For these experiments, we used preparations of isolated TI and TII cells that contained <2% cross-contamination. With a false discovery rate of 1%, 601 genes demonstrated over twofold different expression between TI and TII cells. Those genes with very high levels of differential expression may be useful as markers of cell phenotype and in generating novel hypotheses about functions of TI and TII cells. We found similar numbers of differentially expressed genes between freshly isolated TI or TII cells and cultured TII cells (698, 637 genes) and freshly isolated TI and TII cells (601 genes). Tests of sameness/difference including cluster dendrograms and log/log identity plots indicated major differences between the phenotypes of freshly isolated TI cell and cultured type II cell populations. The latter results suggest that experiments with TII cells cultured under these conditions should be interpreted with caution with respect to biological relevance to TI or TII cells.

Protein transport across the lung epithelial barrier

Alveolar lining fluid normally contains proteins of important physiological, antioxidant, and mucosal defense functions [such as albumin, immunoglobulin G (IgG), secretory IgA, transferrin, and ceruloplasmin]. Because concentrations of plasma proteins in alveolar fluid can increase in injured lungs (such as with permeability edema and inflammation), understanding how alveolar epithelium handles protein transport is needed to develop therapeutic measures to restore alveolar homeostasis. This review provides an update on recent findings on protein transport across the alveolar epithelial barrier. The use of primary cultured rat alveolar epithelial cell monolayers (that exhibit phenotypic and morphological traits of in vivo alveolar epithelial type I cells) has shown that albumin and IgG are absorbed via saturable processes at rates greater than those predicted by passive diffusional mechanisms. In contrast, secretory component, the extracellular portion of the polymeric immunoglobulin receptor, is secreted into alveolar fluid. Transcytosis involving caveolae and clathrin-coated pits is likely the main route of alveolar epithelial protein transport, although relative contributions of these internalization steps to overall protein handling of alveolar epithelium remain to be determined. The specific pathways and regulatory mechanisms responsible for translocation of proteins across lung alveolar epithelium and regulation of the cognate receptors (e.g., 60-kDa albumin binding protein and IgG binding FcRn) expressed in alveolar epithelium need to be elucidated.

Lactoferrin and secretory IgA in the bronchoalveolar lavage fluid from patients with a stable asthma

We have measured lactoferrin and secretory IgA (sIgA) in the unconcentrated bronchoalveolar lavage fluid (BALF) from nonsmoking healthy volunteers (n = 10) and nonsmoking patients with stable asthma (n = 14). The median concentrations and the ranges of lactoferrin were controls, 0.13 mg/L (0.01-0.43 mg/L); asthma, 0.41 mg/L (0.07-7.51 mg/L). For sIgA the results were controls, 0.48 mg/L (0.12-1.47 mg/L); asthma, 1.29 mg/L (0.65-14.6 mg/L). The concentrations in the epithelial lining fluid (ELF) were calculated on the basis of urea in BALF and serum. SIgA and lactoferrin levels in the BALF and ELF from the patients with asthma were higher than in controls (Mann-Whitney U-test, p less than 0.03). Our results indicate that in patients with stable asthma the airway epithelial cells are activated, resulting in an enhanced secretion of lactoferrin and enhanced secretory transport of sIgA into the airway lumen.

A study of human interstitial lung diseases with special reference to immune complexes and hyaline membrane

To evaluate the pathogenetic roles of immune complexes and alveolar hyaline membrane in idiopathic interstitial pneumonia (IIP), immunohistological and ultrastructural studies of the kidney and lung were performed in 23 cases of IIP, 19 cases of autoimmune diseases, 17 cases of interstitial pneumonia other than IIP, and 11 cases of bronchopneumonia as a control group. None of the cases of IIP or interstitial pneumonia other than IIP showed immune complexes in the alveolar and glomerular capillary walls. On the other hand, one case of SLE was positive for IgG and components of complement along the alveolar and glomerular capillary walls. The alveolar hyaline membrane in the present cases revealed immunoglobulins as well as components of complement, which were poorly soluble in chaotropic solution or acidic buffer. These results indicate that circulating immune complexes play a minor role in the pathogenesis of IIP and other types of interstitial pneumonia, and that there is no relationship between immune complex deposition in alveoli and the alveolar hyaline membrane. It is necessary to further investigate factors other than immune complexes involved in alveolar tissue damage and to clarify the significance of the hyaline membrane in the processes occurring from acute changes to pulmonary fibrosis in IIP.

The measuring of "respiratory-membrane permeability" and local production of immunoglobulins and antibodies by means of an analysis of sputum

When measuring the exudation of serum proteins and the local production of immunoglobulins and antibodies within the lung by means of an analysis of sputum, the permeability properties of the respiratory membrane should be taken into account. In this paper, we describe the "loss of size selectivity" that usually accompanies an increased permeability on the part of the respiratory membrane. This phenomenon enables us to measure respiratory membrane permeability independently of the sputum water content. Consequences with regard to discrimination between leakage from the circulation and/or local production of immunoglobulins and antibodies are discussed. Sequential studies which take these factors into account may provide insights into the extent of local inflammatory reactions in individual patients.

Immunohistochemical demonstration of immunoglobulin A in human sebaceous and sweat glands

Immunoglobulin A (IgA) mediated humoral defense mechanisms have been detected on all mucous membrane surfaces. There are only a few papers about the presence of IgA in human skin. In order to demonstrate the occurrence of IgA in sebaceous and sweat glands, biopsies of normal human skin were investigated and compared to intestinal mucosa. Two different commercially available anti-IgA antibodies were used. For light microscopy peroxidase-anti-peroxidase (PAP) or avidin-biotin complex (ABC) staining was used, and for electron microscopy protein-A-gold (PAG) labeling was performed on tissue sections. Specifically decorated IgA was found in sebaceous glands as well as in various portions of eccrine glands. In sebaceous glands, the maximum of IgA concentration was seen near the mouth of pilosebaceous ducts. Sweat ducts exhibited a continuous coat of IgA, whereas secretory portions contained only singular scattered IgA positive cells. Immunoelectron microscopy suggests endocytotic uptake and processing of IgA in the glandular cells. These results indicate strongly that IgA are secreted by normal human sebaceous and sweat glands. Because it is well known that IgA plays an important role in inactivation of invading viruses, bacteria, and other antigenic structures on mucous membranes, it appears that IgA in sebum and sweat fulfil a similar function on the outer body surface.

Immunoelectron microscopical localization of immunoglobulins, secretory component and J chain in the human minor salivary glands

Localization of IgA, secretory component (SC) and J chain was investigated immunocytochemically in minor salivary glands of the lip and palate to define the mechanism involved in the transport of immunoglobulin A (sIgA) into the saliva from the minor salivary glands. SC synthesis was detected in mucous acinar cells and ductal epithelial cells. Free SC is secreted into the saliva through secretory granules in the mucous acinar cells. Dimeric IgA containing J chain is translocated through these cells as sIgA by a SC-mediated transport mechanism involving cytoplasmic vesicles.

Cells containing IgA subclasses in bronchi of subjects with and without chronic obstructive lung disease

Necropsy specimens were obtained from the lungs of 10 subjects who had no history of lung disease, 10 who had died with chronic bronchitis, and 10 with bronchiectasis. Tissue sections were stained for IgA1 or IgA2 using the immunoperoxidase technique, and the number of cells in the bronchi stained for these proteins was counted. The total number of IgA positive cells was increased in bronchitic and bronchiectatic lungs compared with those from control subjects. The number of IgA2 positive cells was similar in those with bronchitis and bronchiectasis and significantly higher than in controls. Similarly, cells containing IgA1 were increased in the lungs of subjects with chest disease but were higher in those with bronchitis than in those with bronchiectasis. The proportion of IgA2:total IgA containing cells was similar in sections from controls (mean (SD) 25 (5.0)%) and those with bronchiectasis (mean (SD) 24 (4)%), but lower in those with bronchitis (mean (SD) 19 (5.0)%). The results show that cells containing IgA1 predominate in the major bronchi but that the proportion of cells containing IgA2 is higher than in non-mucosal lymphoid tissues. Bronchitis and bronchiectasis are associated with greater numbers of cells producing IgA in the bronchi, and this is consistent with increased local production of IgA in the lung secretions of bronchitic subjects.

Glomerular IgA deposition in pulmonary diseases

Glomerular changes of 70 cases of pulmonary diseases and 25 control cases among 1100 consecutive autopsy cases were studied by light, immunofluorescence, and electron microscopy. These pulmonary diseases consisted of 11 cases of chronic obstructive bronchiolitis (COB), 15 cases of bronchopneumonia, 4 cases of acute interstitial pneumonia, 22 cases of idiopathic interstitial pneumonia (IIP), and 18 cases of lung cancer free from IIP. Bacteriological examination of the lung was performed in these cases including control cases on autopsy. Mesangial IgA deposition was predominant in 25 out of the 70 study cases (36%) frequently accompanied by C3, whereas slight mesangial IgA deposition was observed in one of the control cases. Incidence of IgA deposition was 64% in IIP, 54.5% in COB, 13.3% in bronchopneumonia, 16.7% in lung cancer and 25% in acute interstitial pneumonia. The results of the present study suggest that recurrence or persistence of inflammatory processes of the lung leads to IgA-mediated immune abnormalities and to mild mesangial changes with predominant IgA deposition, which are similar to the immunopathologic features of IgA nephropathy.

Immunohistochemical study of so-called sclerosing haemangioma of the lung

To elucidate the histogenesis of sclerosis haemangioma of the lung, we examined 7 cases with the immunoperoxidase method using antibodies against several useful marker antigens; secretory component (SC), cytokeratins, epithelial membrane antigen (EMA) for epithelial cells, factor VIII related antigens (factor VIII) for endothelial cells, vimentin and desmin for mesenchymal cells. The results were compared with those of histologically normal lung tissues. Both the characteristic round cells arranged in sheets, which are present predominantly in the solid area and are reported to be neoplastic, and the flattened cells lining blood lakes show positive staining for EMA only, with negative staining for the other marker antigens. These observations suggest that these cells are derived from epithelium rather than mesothelium or from endothelium, and are analogous to type I pneumocytes. This conclusion is supported by their immunohistochemical characteristics, in comparison with the localization patterns of the marker antigens in normal lung tissues. However, the lining epithelial cells of papillary projections in the papillary area and of ducts in the solid area stained for SC and cytokeratins as well as EMA, and their immunohistochemical characteristics are analogous to those of bronchiolar epithelial cells or type II pneumocytes in normal lung tissues.