Immunoglobulin levels in bronchoalveolar lavage fluid of children with chronic chest disease

Rheumatoid Arthritis-Specific Autoimmunity in the Lung Before and at the Onset of Disease

OBJECTIVE

The lung is implicated as a site for breach of tolerance prior to onset of seropositive rheumatoid arthritis (RA). To substantiate this, we investigated lung-resident B cells in bronchoalveolar lavage (BAL) samples from untreated early RA patients and anti-citrullinated protein antibody (ACPA)-positive individuals at risk for developing RA.

METHODS

Single B cells (n = 7,680) were phenotyped and isolated from BAL samples from individuals at risk of RA (n = 3) and at RA diagnosis (n = 9). The immunoglobulin variable region transcripts were sequenced and selected for expression as monoclonal antibodies (n = 141). Monoclonal ACPAs were tested for reactivity patterns and binding to neutrophils.

RESULTS

Using our single-cell approach, we found significantly increased proportions of B lymphocytes in ACPA+ compared to ACPA- individuals. Memory and double-negative B cells were prominent in all subgroups. Upon antibody re-expression, 7 highly mutated citrulline-autoreactive clones originating from different memory B cell subsets were identified, both in individuals at risk of RA and early RA patients. Lung IgG variable gene transcripts from ACPA+ individuals carried frequent mutation-induced N-linked Fab glycosylation sites (P < 0.001), often in the framework 3 of the variable region. Two of the lung ACPAs bound to activated neutrophils, 1 from an individual at risk of RA and 1 from an early RA patient.

CONCLUSION

T cell-driven B cell differentiation resulting in local class switching and somatic hypermutation are evident in lungs before as well as in early stages of ACPA+ RA. Our findings add to the notion of lung mucosa being a site for initiation of citrulline autoimmunity preceding seropositive RA.

Effect of Lavage Solution Type on Bronchoalveolar Lavage Fluid Cytology in Clinically Healthy Horses

Equine bronchoalveolar lavage (BAL) is usually performed with 250-500 mL of isotonic saline at pH 5.5. The acidic pH of saline may cause an increase in airway neutrophil count 48 h after BAL. Other isotonic solutions such as Ringer's solution, phosphate-buffered saline (PBS) or Plasma-Lyte 148® have a neutral pH of 7.4 and might be a better choice for BAL by not provoking inflammation and the influx of neutrophils into airways. BAL was performed in four healthy horses in four different lung lobes using four different solutions in a randomized crossover design. In each lobe, BAL was performed twice with a 48 h interval using 250 mL of solution. Automated total nucleated cell counts (TNCs) were recorded, and differential cell counts in lavage fluid were determined by two investigators blinded to treatments. The mean volume of BAL fluid retrieved was 51 ± 14%. The mean neutrophil percentage (%N) increased from 1.5 ± 0.9% to 14.7 ± 9.6% at 48 h (p < 0.001) but was not significantly affected by the solution used or the lung lobe sampled. In conclusion, in this study, the influx of neutrophils into airways after BAL was independent of the type of isotonic solution used and the lung lobe sampled. Saline remains an appropriate solution for BAL in horses.

Half-life extension of efficiently produced DARPin serum albumin fusions as a function of FcRn affinity and recycling

Serum albumin shows slow clearance from circulation due to neonatal Fc receptor (FcRn)-mediated recycling and has been used for half-life extension. We report here fusions to a high-affinity DARPin, binding to Epithelial Cell Adhesion Molecule (EpCAM). We developed a novel, efficient expression system for such fusion proteins in Pichia pastoris with titers above 300 mg/L of lab-scale shake-flask culture. Since human serum albumin (HSA) does not bind to the murine FcRn, half-lives of therapeutic candidates are frequently measured in human FcRn transgenic mice, limiting useable tumor models. Additionally, serum albumins with extended half-life have been designed. We tested HSA7, motivated by its previously claimed extraordinarily long half-life in mice, which we could not confirm. Instead, we determined a half-life of only 29 h for HSA7, comparable to MSA. The fusion of HSA7 to a DARPin showed a similar half-life. To rationalize these findings, we measured binding kinetics and affinities to murine and human FcRn. Briefly, HSA7 showed affinity to murine FcRn only in the micromolar range, comparable to MSA to its cognate murine FcRn, and an affinity in the nanomolar range only to the human FcRn. This explains the comparable half-life of MSA and HSA7 in mice, while wild-type-HSA has a half-life of only 21 h, as it does not bind the murine FcRn and is not recycled. Thus, HSA-fusions with improved FcRn-affinity, such as HSA7, can be used for preclinical experiments in mice when FcRn transgenes cannot be used, as they reflect better the complex FcRn-mediated recycling and distribution mechanisms.

Polyvalent Immunoglobulin as a Potential Treatment Option for Patients with Recurrent COPD Exacerbations

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation and episodes of worsening respiratory symptoms and pulmonary function, termed acute exacerbations of COPD (AECOPD). AECOPD episodes are associated with heightened airway inflammation and are often triggered by infection. A subset of COPD patients develops frequent exacerbations despite maximal existing standard medical therapy. It is therefore clear that a targeted and more effective prevention strategy is needed. Immunoglobulins are glycoprotein molecules that are secreted by B lymphocytes and plasma cells and play a critical role in the adaptive immune response against many pathogens. Altered serum immunoglobulin levels have been observed in patients with immunodeficiencies and inflammatory diseases. Serum immunoglobulin has also been identified as potential biomarkers of AECOPD frequency. Since plasma-derived polyvalent immunoglobulin treatment is effective in preventing recurrent infections in immunodeficient patients and in suppressing inflammation in many inflammatory diseases, it may be conceivable that immunoglobulin treatment may be effective in preventing recurrent AECOPD. In this article, we provide a review of the current knowledge on immunoglobulin treatment in patients with COPD and discuss plausible mechanisms as to how immunoglobulin treatment may work to reduce AECOPD frequency.

The neonatal Fc receptor in mucosal immune regulation

The neonatal Fc receptor (FcRn) was first recognized for its role in transfer of maternal IgG to the foetus or newborn, providing passive immunity early in life. However, it has become clear that the receptor is versatile, widely expressed and plays an indispensable role in both immunological and non-immunological processes throughout life. The receptor rescues immunoglobulin G (IgG) and albumin from intracellular degradation and shuttles the ligands across polarized cell barriers, in all cases via a pH-dependent binding-and-release mechanism. These processes secure distribution and high levels of both IgG and albumin throughout the body. At mucosal sites, FcRn transports IgG across polarized epithelial cells where it retrieves IgG in complex with luminal antigens that is delivered to tissue-localized immune cells. In dendritic cells (DCs), FcRn orchestrates processing of IgG-opsonized immune complexes (ICs) in concert with classical Fcγ receptors, which results in antigen presentation and cross-presentation of antigenic peptides on MHC class II and I to CD4+ and CD8+ T cells, respectively. Hence, FcRn regulates transport of the ligands within and across different types of cells, but also processing of IgG-ICs by immune cells. As such, the receptor is involved in immune surveillance and protection against infections. In this brief review, we highlight how FcRn expressed by hematopoietic and non-hematopoietic cells contributes to immune regulation at mucosal barriers-biology that can be utilized in development of biologics and subunit vaccines for non-invasive delivery.

Enhanced FcRn-dependent transepithelial delivery of IgG by Fc-engineering and polymerization

Monoclonal IgG antibodies (Abs) are used extensively in the clinic to treat cancer and autoimmune diseases. In addition, therapeutic proteins are genetically fused to the constant Fc part of IgG. In both cases, the Fc secures a long serum half-life and favourable pharmacokinetics due to its pH-dependent interaction with the neonatal Fc receptor (FcRn). FcRn also mediates transport of intact IgG across polarized epithelial barriers, a pathway that is attractive for delivery of Fc-containing therapeutics. So far, no study has thoroughly compared side-by-side how IgG and different Fc-fusion formats are transported across human polarizing epithelial cells. Here, we used an in vitro cellular transport assay based on the human polarizing epithelial cell line (T84) in which both IgG1 and Fc-fusions were transported in an FcRn-dependent manner. Furthermore, we found that the efficacy of transport was dependent on the format. We demonstrate that transepithelial delivery could be enhanced by Fc-engineering for improved FcRn binding as well as by Fc-polymerization. In both cases, transport was driven by pH-dependent binding kinetics and the pH at the luminal side. Hence, efficient transcellular delivery of IgG-based drugs across human epithelial cells requires optimal pH-dependent FcRn binding that can be manipulated by avidity and Fc-engineering, factors that should inspire the design of future therapeutics targeted for transmucosal delivery.

The role of albumin receptors in regulation of albumin homeostasis: Implications for drug delivery

Albumin is the most abundant protein in blood and acts as a molecular taxi for a plethora of small insoluble substances such as nutrients, hormones, metals and toxins. In addition, it binds a range of medical drugs. It has an unusually long serum half-life of almost 3weeks, and although the structure and function of albumin has been studied for decades, a biological explanation for the long half-life has been lacking. Now, recent research has unravelled that albumin-binding cellular receptors play key roles in the homeostatic regulation of albumin. Here, we review our current understanding of albumin homeostasis with a particular focus on the impact of the cellular receptors, namely the neonatal Fc receptor (FcRn) and the cubilin-megalin complex, and we discuss their importance on uses of albumin in drug delivery.

Unraveling the Interaction between FcRn and Albumin: Opportunities for Design of Albumin-Based Therapeutics

The neonatal Fc receptor (FcRn) was first found to be responsible for transporting antibodies of the immunoglobulin G (IgG) class from the mother to the fetus or neonate as well as for protecting IgG from intracellular catabolism. However, it has now become apparent that the same receptor also binds albumin and plays a fundamental role in homeostatic regulation of both IgG and albumin, as FcRn is expressed in many different cell types and organs at diverse body sites. Thus, to gain a complete understanding of the biological function of each ligand, and also their distribution in the body, an in-depth characterization of how FcRn binds and regulates the transport of both ligands is necessary. Importantly, such knowledge is also relevant when developing new drugs, as IgG and albumin are increasingly utilized in therapy. This review discusses our current structural and biological understanding of the relationship between FcRn and its ligands, with a particular focus on albumin and design of albumin-based therapeutics.

IL-33-dependent induction of allergic lung inflammation by FcγRIII signaling

Atopic asthma is a chronic inflammatory disease of the lungs generally marked by excessive Th2 inflammation. The role of allergen-specific IgG in asthma is still controversial; however, a receptor of IgG-immune complexes (IgG-ICs), FcγRIII, has been shown to promote Th2 responses through an unknown mechanism. Herein, we demonstrate that allergen-specific IgG-ICs, formed upon reexposure to allergen, promoted Th2 responses in two different models of IC-mediated inflammation that were independent of a preformed T cell memory response. Development of Th2-type airway inflammation was shown to be both FcγRIII and TLR4 dependent, and T cells were necessary and sufficient for this process to occur, even in the absence of type 2 innate lymphoid cells. We sought to identify downstream targets of FcγRIII signaling that could contribute to this process and demonstrated that bone marrow-derived DCs, alveolar macrophages, and respiratory DCs significantly upregulated IL-33 when activated through FcγRIII and TLR4. Importantly, IC-induced Th2 inflammation was dependent on the ST2/IL-33 pathway. Our results suggest that allergen-specific IgG can enhance secondary responses by ligating FcγRIII on antigen-presenting cells to augment development of Th2-mediated responses in the lungs via an IL-33-dependent mechanism.

The contribution of allergen-specific IgG to the development of th2-mediated airway inflammation

In both human asthmatics and animal models of allergy, allergen-specific IgG can contribute to Th2-mediated allergic inflammation. Mouse models have elucidated an important role for IgG and Fc-gamma receptor (FcγR) signaling on antigen presenting cells (APC) for the induction of airway inflammation. These studies suggest a positive feedback loop between IgG produced by the adaptive B cell response and FcγR signaling on innate immune cells. Studies of IgG and FcγRs in humans with asthma or allergic lung disease have been more controversial. Some reports have identified associations between allergen-specific IgG and severity of allergic responses, while other studies have found associations of IgG subclass IgG4 with allergic tolerance. In this paper, we review the literature to help define the nature of IgG and FcγR signaling on innate immune cells and how it contributes to the development of allergic immune responses.

Disease surveillance using bronchoalveolar lavage

The role of pulmonary infection and inflammation in the pathogenesis of destructive lung disease in cystic fibrosis (CF) is undisputed. The use of bronchoscopy and bronchoalveolar lavage (BAL) has demonstrated that these processes may begin early in life and be present in the absence of overt clinical symptoms. Some children diagnosed following newborn screening can be infected with Pseudomonas aeruginosa in infancy. Studies using BAL have demonstrated a relationship between lower airway inflammation and bacterial load in the lungs; however, inflammation may occur in the absence of obvious current infection. BAL has the potential to provide a greater understanding of the pathogenesis of CF lung disease and microbiological surveillance provides the opportunity for early detection and eradication of P. aeruginosa. Lack of standardization inhibits the ability to compare data from different centres and to optimize treatment strategies. This review discusses the recommendations from a workshop held in early 2007 aimed at achieving a standardized approach to BAL in infants and young children with CF.

The secretory immunoglobulin A response to Mycobacterium tuberculosis in a childhood population

We report on the measurement of saliva anti-Purified Protein Derivative sIgA and 38kDa antibodies from 127 children, of whom 31 were strong tuberculosis suspects and 96 were healthy contact children. The results concerning the percentage of children with antibody reactivity to PPD and 38kDa antigens showed that, of these 2 antigens, 38kDa induced higher reactivity in patients positive and negative for the Tuberculin Skin Test (28% and 16.6%, respectively) in comparison to controls positive and negative for the TST (11.7% and 7.1%, respectively). There was a statistically significant difference between patients positive and controls negative for the TST. In relation to the Purified Protein Derivative antigen, while 14.2% of patients positive for the TST showed antibody reactivity to the PPD antigen, no patients negative for the TST had reactivity to this antigen. The findings suggest that these two antigens seem be associated with a different development of the mucosal defence mechanisms mediated by sIgA against Mycobacterium tuberculosis.

Immunoglobulins and inflammatory cytokines in nasal secretions in humoral immunodeficiencies

OBJECTIVE

Chronic respiratory tract infections are a common problem in patients with severe humoral immunodeficiency despite intravenous immunoglobulin therapy (IVIG), often presenting as rhinosinusitis.

METHODS

Because it is unclear whether IVIG is a good substitute at the mucosal surface, we analyzed immunoglobulin levels and inflammatory cytokines (ECP, IL-8, and TNF-alpha) in nasal secretions of 13 patients with common variable immunodeficiency (CVID) and in 10 patients with IgA deficiency.

RESULTS

In patients with CVID, median IgG and IgM levels did not differ significantly from controls, whereas inflammatory cytokines were markedly elevated, reflecting persistent inflammation at the mucosal site. In contrast, patients with IgA deficiency showed significantly raised IgG and IgM levels, whereas ECP and TNF-alpha were only slightly increased.

CONCLUSION

Low levels of SIgA might be compensated locally at the mucosal site by high levels of IgM and IgG. Our findings implicate that adequate IVIG is not sufficient to prevent chronic inflammation of the sinuses in patients with severe humoral immunodeficiency.

Subtle immunodeficiency in severe asthma: IgA and IgG2 correlate with lung function and symptoms

BACKGROUND

Atopy, increased serum IgE and eosinophilic airway inflammation are common in asthma and may indicate aberrant immune responses, but the cause(s) are unknown. It was hypothesized that differences in serum immunoglobulins, immunoglobulin free light chains (FLC) and secretory IgA (sIgA) would exist between subjects with asthma of varying severity and normal subjects, and the levels would correlate with lung function, symptoms and airway inflammation.

METHODS

Serum IgG, IgA, IgE and IgM, IgG subclasses and FLC, and bronchoalveolar lavage sIgA were evaluated from 15 normal subjects, 9 mild and 22 severe asthmatics with similar atopic status. Asthma symptoms were obtained by questionnaire, and airway inflammation was assessed by immunostaining for five inflammatory cell types.

RESULTS

Immunoglobulin levels in all groups were generally within the normal range. However, IgA and IgG were lower in severe asthmatics than normal subjects (overall p = 0.006 and 0.02, respectively). IgA, but not IgG, correlated with lung function and asthma symptoms (r-values >0.58; p-values <0.009). Although similar among the groups, higher sIgA and IgG(2) also positively correlated with lung function and negatively with asthma symptoms (r-values >0.63; p-values <0.009). IgA and IgG/IgG(1) positively correlated with tissue mast cells.

CONCLUSIONS

Subtle alterations in IgA- and IgG(2)-mediated responses in asthma may be disease-related. As their levels are generally normal, it is possible that the quality/repertoire of immune protection provided by these isotypes, perhaps against carbohydrate epitopes, may be altered in asthma.

Expression and Transport Functionality of FcRn within Rat Alveolar Epithelium: A Study in Primary Cell Culture and in the Isolated Perfused Lung

PURPOSE

The neonatal constant region fragment receptor (FcRn) binds and transports IgG. FcRn expression in the upper tracheobronchial airways of the lung is recognized. In this study, we sought to characterize the functional expression of FcRn within alveolar regions of lung tissue.

METHODS

FcRn immunohistochemistry was performed on intact rat lung. FcRn expression [Western blot, reverse transcription-polymerase chain reaction (RT-PCR), and immunofluorescence microscopy] and IgG transport functionality were assessed in an in vitro rat alveolar epithelial primary cell culture model. An isolated perfused rat lung model was used to examine IgG transport across pulmonary epithelium from airspace to perfusate.

RESULTS

FcRn is expressed in intact alveolar epithelium, substantiated by expression and functionality in an in vitro alveolar epithelial model within which IgG transport was temperature sensitive, concentration dependent, and inhibited by excess unlabeled IgG and, to a disproportionate level, by anti-FcRn antibody. Saturable IgG transport across pulmonary epithelium was evident in an isolated perfused rat lung, inhibitable by competing IgG, and displayed a relatively low maximal net IgG absorptive rate of approximately 80 ng/h.

CONCLUSION

Pulmonary epithelium expresses functional FcRn providing an absorption pathway potentially important for highly potent Fcgamma-fusion proteins but unlikely to be of quantitative significance for the systemic delivery of inhaled therapeutic monoclonal IgGs.

Low levels of immunoglobulin A in children with intrinsic asthma: a possible protection against atopy

Immunoglobulin A and G (IgA, IgG) serum concentrations were detected in children with nonallergic/intrinsic (36 children) or allergic/extrinsic asthma (43 children) and in age-matching control children (40 children). Asthmatic children with allergic asthma had lower IgA (1.36+/-0.54 g/L) and higher IgG (10.48+/-2.77 g/L) levels than the age-matching control children group (1.63+/-0.69 vs. 9.01+/-2.32 g/L). Children with nonallergic/intrinsic asthma had lower IgA (1.03+/-0.41 g/L) ( p = 0.004) and IgG (8.38+/-1.93 g/L) (p = 0.001) levels than the allergic/extrinsic asthma group (1.36+/-0.54 vs. 10.48+/-2.77 g/L). Low IgA levels were found in children with nonallergic/intrinsic asthma and high IgG levels were found in those children with allergic/extrinsic childhood asthma. The hypothesis is that the increased incidence of asthma in the population may be caused by a decrease in childhood infections (hygiene hypothesis). Frequent infections in early life boost the immune system, stimulating Th1-type response in young children and reducing the risk of atopic diseases. Our hypothesis is that low IgA (and/or IgG) levels in our patients might be responsible for infection development among those children with nonallergic/intrinsic asthma. These infections stimulate the normal development of immune system in young children, reducing risk of atopy, so that those children do not get allergic/extrinsic childhood asthma. Intrinsic childhood asthma=nonallergic (nonatopic) childhood asthma. Extrinsic childhood asthma=allergic (atopic) childhood asthma.

Prospective observational study of antiphospholipid antibodies in acute lung injury and acute respiratory distress syndrome: comparison with catastrophic antiphospholipid syndrome

Detection of antiphospholipid (aPL) antibodies in bronchoalveolar lavage fluid (BALF) of patient with acute respiratory distress syndrome (ARDS) suggests involvement of autoimmune mechanisms in the pathogenesis of ARDS. We investigated whether aPL antibodies could be detected in the serum as well as BALF of patients with acute lung injury (ALI) and ARDS. IgG anticardiolipin, IgG anti-beta2-glycoprotein I, IgG antiphosphatidic acid and IgG antiphosphatidylserine antibodies were detected by ELISA in low titers within the normal range in the BALF and serum of nine patients with ALI and 17 patients with ARDS. However, one out of 27 patients investigated had high levels of aPL antibodies in both BALF and serum. This patient suffered from severe ARDS due to sepsis. The high aPL antibody levels in serum possibly triggered by sepsis were associated with high aPL antibody levels in BALF, which can be explained by high capillary-alveolar permeability. Computed tomography scan revealed widespread infarctions in brain, spleen and kidneys, and pulmonary thromboembolism, suggesting the diagnosis of catastrophic antiphospholipid syndrome.

Immunoglobulin transport across polarized epithelial cells

IgA, IgG and IgM are transported across epithelial cells in a receptor-mediated process known as transcytosis. In addition to neutralizing pathogens in the lumen of the gastrointestinal, respiratory and urogenital tracts, these antibody-receptor complexes are now known to mediate intracellular neutralization of pathogens and might also be important in immune activation and tolerance. Recent studies on the intracellular transport pathways of antibody-receptor complexes and antibody-stimulated receptor-mediated transcytosis are providing new insight into the nature and regulation of endocytic pathways.

Receptor-mediated immunoglobulin G transport across mucosal barriers in adult life: functional expression of FcRn in the mammalian lung

Mucosal secretions of the human gastrointestinal, respiratory, and genital tracts contain the immunoglobulins (Ig)G and secretory IgA (sIgA) that function together in host defense. Exactly how IgG crosses epithelial barriers to function in mucosal immunity remains unknown. Here, we test the idea that the MHC class I-related Fc-receptor, FcRn, transports IgG across the mucosal surface of the human and mouse lung from lumen to serosa. We find that bronchial epithelial cells of the human, nonhuman primate, and mouse, express FcRn in adult-life, and demonstrate FcRn-dependent absorption of a bioactive Fc-fusion protein across the respiratory epithelium of the mouse in vivo. Thus, IgG, like dimeric IgA, can cross epithelial barriers by receptor-mediated transcytosis in adult animals. These data show that mucosal surfaces that express FcRn reabsorb IgG and explain a mechanism by which IgG may act in immune surveillance to retrieve lumenal antigens for processing in the lamina propria or systemically.