Surface phenotype of Langerhans cells and lymphocytes in granulomatous lesions from patients with pulmonary histiocytosis X

New insights in lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis

Lymphangioleiomyomatosis (LAM) and pulmonary Langerhans cell histiocytosis (PLCH) are rare diseases that lead to progressive cystic destruction of the lungs. Despite their distinctive characteristics, these diseases share several features. Patients affected by LAM or PLCH have similar radiological cystic patterns, a similar age of onset, and the possibility of extrapulmonary involvement. In this review, the recent advances in the understanding of the molecular pathogenesis, as well as the current and most promising biomarkers and therapeutic approaches, are described.

Understanding of LAM/PLCH pathogenesis has improved over the past years, leading to new therapeutic approacheshttp://ow.ly/7wjR30erSJY

Current understanding and management of pulmonary Langerhans cell histiocytosis

Pulmonary Langerhans cell histiocytosis (PLCH) is a diffuse lung disease that usually affects young adult smokers. PLCH affects different lung compartments; bronchiolar, interstitial and pulmonary vascular dysfunction may coexist to varying extents, resulting in diverse phenotypes. Analyses of PLCH tissues have identified activating mutations of specific mitogen-activated protein kinases (BRAF^V600E and others). The current consensus is that PLCH represents a myeloid neoplasm with inflammatory properties: the myeloid tumour cells exhibit surface CD1a expression and up to 50% of the cells harbour activating BRAF or other MAPK mutations. PLCH may be associated with multisystem disease. The detection of disease outside of the thorax is facilitated by whole body positron emission tomography. The natural history of PLCH is unpredictable. In some patients, disease may remit or stabilise following smoking cessation. Others develop progressive lung disease, often associated with evidence of airflow limitation and pulmonary vascular dysfunction. Due to the inability to accurately predict the natural history, it is important that all patients undergo longitudinal follow-up at least twice a year for the first few years following diagnosis. The treatment of PLCH is challenging and should be individualised. While there is no general consensus regarding the role of immunosuppression or chemotherapy in management, selected patients may experience improvement in lung function with therapy. Determination of BRAF^V600E or other mutations may assist with the development of an individualised approach to therapy. Patients with progressive disease should be referred to specialised centres and considered for a trial of pharmacotherapy or evaluated for transplantation.

Pulmonary Langerhans Cell Histiocytosis: An Update From the Pathologists' Perspective

CONTEXT

Pulmonary Langerhans cell histiocytosis (PLCH) is a rare histiocytic disorder that almost exclusively affects the lungs of smokers. PLCH is characterized by bronchiolocentric nodules and/or cysts in an upper and mid lung distribution with sparing of the costophrenic angles. The diagnosis can be challenging and often requires transbronchial biopsy or surgical lung biopsy. Pulmonary hypertension is a relatively common and sometimes severe complication of PLCH. The pathogenesis of PLCH is still debated. Recently, BRAF V600E mutation and BRAF expression have been identified in some patients with PLCH, suggesting that at least a subset of PLCH has a clonal proliferation. While smoking cessation is the first-line treatment of PLCH, some patients might require additional treatment and eventually transplant. Given that the lesional cells of PLCH express BRAF in some patients, MAPKinase pathway-targeted treatment might be useful for therapy-resistant patients.

OBJECTIVE

To present the more recently recognized clinical and pathologic aspects of PLCH, including pulmonary hypertension in PLCH, pathogenesis, and treatment, as well as the basic diagnostic approach to PLCH.

DATA SOURCES

Authors' own research, and search of literature database (PubMed) and UpToDate.

CONCLUSIONS

Despite the recent progress, more studies are needed to elucidate the biology of PLCH for identification of prognostic factors and appropriate treatment options, especially for therapy-refractory PLCH cases.

Severe pulmonary hypertension in adult pulmonary Langerhans cell histiocytosis: the effect of sildenafil as a bridge to lung transplantation

Severe pulmonary hypertension (PH) often develops in patients with pulmonary Langerhans cell histiocytosis (PLCH). Supplemental oxygen treatment is often used, whereas pulmonary arterial hypertension-specific vasodilators are generally considered hazardous because of the possible development of pulmonary edema and deterioration of hypoxia. In the present report, we herein describe a PLCH patient with severe PH in whom sildenafil, a phosphodiesterase 5 (PDE5) inhibitor, substantially improved the pulmonary hemodynamics before lung transplantation. An immunohistochemical study of the resected lung revealed positive staining for PDE5 on the diseased pulmonary arteries. These observations suggest that sildenafil can be a promising therapeutic option for PH in patients with PLCH.

World Health Organization group 5 pulmonary hypertension

World Health Organization (WHO) group 5 pulmonary hypertension (PH) entails a heterogeneous group of disorders that may cause PH by unclear and/or multiple mechanisms. In particular, group 5 includes PH caused by hematologic disorders, systemic diseases, metabolic disorders, chronic renal failure, and disorders leading to pulmonary vascular occlusion or compression. This article discusses common pathogenic mechanisms leading to group 5 PH, followed by a detailed overview of epidemiology, pathogenesis, and disease-specific management of the individual group 5 conditions. Off-label use of vasomodulatory therapies, typically indicated for pulmonary arterial hypertension (WHO group 1 PH), in group 5 conditions is also discussed.

Pulmonary langerhans cell histiocytosis

Pulmonary Langerhans Cell Histiocytosis (PLCH) is a relatively uncommon lung disease that generally, but not invariably, occurs in cigarette smokers. The pathologic hallmark of PLCH is the accumulation of Langerhans and other inflammatory cells in small airways, resulting in the formation of nodular inflammatory lesions. While the overwhelming majority of patients are smokers, mechanisms by which smoking induces this disease are not known, but likely involve a combination of events resulting in enhanced recruitment and activation of Langerhans cells in small airways. Bronchiolar inflammation may be accompanied by variable lung interstitial and vascular involvement. While cellular inflammation is prominent in early disease, more advanced stages are characterized by cystic lung destruction, cicatricial scarring of airways, and pulmonary vascular remodeling. Pulmonary function is frequently abnormal at presentation. Imaging of the chest with high resolution chest CT scanning may show characteristic nodular and cystic abnormalities. Lung biopsy is necessary for a definitive diagnosis, although may not be required in instances were imaging findings are highly characteristic. There is no general consensus regarding the role of immunosuppressive therapy in smokers with PLCH. All smokers must be counseled on the importance of smoking cessation, which may result in regression of disease and obviate the need for systemic immunosuppressive therapy. The prognosis for most patients is relatively good, particularly if longitudinal lung function testing shows stability. Complications like pneumothoraces and secondary pulmonary hypertension may shorten life expectancy. Patients with progressive disease may require lung transplantation.

Smoking-related interstitial lung diseases

Cigarette smoke, a toxic collection of thousands of chemicals generated from combustion of tobacco, is recognized as the primary causative agent of certain diffuse interstitial and bronchiolar lung diseases. Most patients afflicted with these disorders are cigarette smokers, and smoking cessation has been shown to be capable of inducing disease remission and should occupy a pivotal role in the management of all smokers with these diffuse lung diseases. The role of pharmacotherapy with corticosteroids or other immunomodulating agents is not well established but may be considered in patients with progressive forms of smoking-related interstitial lung diseases.

Rare lung diseases III: pulmonary Langerhans' cell histiocytosis

Pulmonary Langerhans' cell histiocytosis (PLCH) is an unusual cystic lung disease that is also characterized by extrapulmonary manifestations. The current review discusses the presenting features and relevant diagnostic testing and treatment options for PLCH in the context of a clinical case. While the focus of the present article is adult PLCH and its pulmonary manifestations, it is important for clinicians to distinguish the adult and pediatric forms of the disease, as well as to be alert for possible extrapulmonary complications. A major theme of the current series of articles on rare lung diseases has been the translation of insights gained from fundamental research to the clinic. Accordingly, the understanding of dendritic cell biology in this disease has led to important advances in the care of patients with PLCH.

Histiocytic disorders of the lung

Histiocytic proliferations involving the lung span a broad spectrum. Some proliferations are primary; others represent a histiocytic response secondary to conditions in which there may be isolated lung involvement or the lung may be involved as part of a systemic process. Primary histiocytic lung disorders, particularly those of uncertain histogenesis are a heterogeneous and intriguing group of disorders. Although they have been the focus of attention by clinicians and pathologists alike, much is unknown about their etiopathogenesis. Owing to this uncertainty, our understanding of these processes is in a state of flux, and is likely to change as more information is brought to light. This review will focus on pulmonary histiocytic proliferations of uncertain histogenesis. Other histiocytic lesions will be dealt with in brief.

Smoking-related interstitial lung disease

Pulmonary diseases associated with tobacco smoking are a complex group of disorders ranging from chronic obstructive pulmonary disease (COPD) to lung cancer. Interstitial lung diseases (ILDs) have only recently been linked to smoking. The ILDs related to smoking include respiratory bronchiolitis-associated interstitial lung disease, desquamative interstitial pneumonia, and pulmonary Langerhans cell histiocytosis. The relationship of smoking with each of these entities has been largely established on the weight of epidemiologic evidence. Although they have been retained as distinct and separate conditions in various classifications of interstitial lung diseases, these 3 entities share a number of clinical, radiologic, and pathologic features suggesting that they represent a spectrum of patterns of interstitial lung disease occurring in predisposed individuals who smoke. Evaluation of histologic features, particularly in surgical lung biopsy samples, is important in making the distinction between these disorders. However, even after tissue biopsy, it may sometimes be difficult to clearly separate these entities. The importance of making the distinction between them lies in the different clinical management strategies used. Further experimental evidence, including genetic information, may be important in improving our understanding of these diseases.

Molecular Basis of Pulmonary Disease

Pulmonary pathology includes a large spectrum of both neoplastic and non-neoplastic diseases that affect the lung. Many of these are a result of the unusual relationship of the lung with the outside world. Every breath that a human takes brings the outside world into the body in the form of infectious agents, organic and inorganic particles, and noxious agents of all types. Although the lung has many defense mechanisms to protect itself from these insults, these are not infallible; therefore, lung pathology arises. Damage to the lung is particularly important given the role of the lung in the survival of the organism. Any impairment of lung function has widespread effects throughout the body, since all organs depend on the lungs for the oxygen they need. Pulmonary pathology catalogs the changes in the lung tissues and the mechanisms through which these occur. This chapter presents a review of lung pathology and the current state of knowledge about the pathogenesis of each disease. It suggests that a clear understanding of both morphology and mechanism is required for the development of new therapies and preventive measures.

Challenges in pulmonary fibrosis. 3: Cystic lung disease

Cystic lung disease is a frequently encountered problem caused by a diverse group of diseases. Distinguishing true cystic lung disease from other entities, such as cavitary lung disease and emphysema, is important given the differing prognostic implications. In this paper the features of the cystic lung diseases are reviewed and contrasted with their mimics, and the clinical and radiographic features of both diffuse (pulmonary Langerhans' cell histiocytosis and lymphangioleiomyomatosis) and focal or multifocal cystic lung disease are discussed.

Natural Course of Isolated Pulmonary Langerhans’ Cell Histiocytosis in a Toddler

Isolated pulmonary Langerhans' cell histiocytosis (LCH) is distinctly rare under the age of 15 years, since the majority of patients are young adult males with heavy smoking habits. Isolated pulmonary involvement suggests that antigens inhaled from cigarette smoke are involved. Here we present a case of LCH restricted to the lungs in a toddler whose parents were heavy smokers. Since LCH was not medically treated for 3 years due to parental refusal, the disease can be regarded as having followed its natural course. During the 3-year follow-up, the disease progressed to severe pulmonary fibrosis resulting in honeycomb lungs. Based on the comparative immunohistochemical analyses of the cells obtained from bronchoalveolar lavages during the disease course, it appears that the evolution of fibrosis is rather a result from the accumulating alveolar macrophages than from the persistence of the Langerhans' cells. Passive cigarette smoking may be considered a significant risk factor in both the pathogenesis and development of pulmonary LCH in a small child.

Expression of apoptosis-regulatory proteins in lesions of pulmonary Langerhans cell histiocytosis

AIMS

Pulmonary Langerhans cell histiocytosis (PLCH) is characterized by the presence of lesions containing numerous activated Langerhans cells (LCs). An uncontrolled immune response sustained by activated LCs seems to be involved in the pathogenesis of the disease. The aim of this study was to establish whether disruption of LC apoptosis related to the expression of the Bcl-2 family proteins is implicated in the maintenance of PLCH lesions.

METHODS

Six patients with PLCH were evaluated by morphological and immunohistochemical techniques to explore the incidence of apoptosis in pathological LCs and to characterize the expression of Bcl-2-related proteins by these cells.

RESULTS

Very few LCs present in PLCH lesions exhibited nuclear apoptotic changes or expressed cleaved caspase-3, whereas they all strongly expressed the anti-apoptotic molecule Bcl-x(L). Interestingly, pulmonary LCs present in intervening lung tissue not involved by the pathological process and known to be immature dendritic cells did not express Bcl-2 family proteins.

CONCLUSIONS

These findings suggest that activated LCs present within PLCH lesions are poorly susceptible to apoptosis and, thus, are able to sustain the pathological process by causing continuous local stimulation of T cells. Functional studies are needed, however, to demonstrate that they are actually resistant to programmed cell death.

From the Archives of the AFIP

Pulmonary Langerhans cell histiocytosis (PLCH) is an isolated form of Langerhans cell histiocytosis that primarily affects cigarette smokers. PLCH is characterized by peribronchiolar proliferation of Langerhans cell infiltrates that form stellate nodules. The nodular lesions frequently cavitate and form thick- and thin-walled cysts, which are thought to represent enlarged airway lumina. PLCH lesions display temporal microscopic heterogeneity, with progression from dense cellular nodules to apparently cavitary nodules to increasing degrees of fibrosis that may extend along alveolar walls. In advanced cases, fibrotic scars are surrounded by enlarged, distorted air spaces. Affected patients are typically young adults who often present with cough and dyspnea. The characteristic radiographic features of PLCH are bilateral nodular and reticulonodular areas of opacity that predominantly involve the upper and middle lung zones with relative sparing of the lung bases. High-resolution computed tomography (CT) shows nodules and cysts in the same distribution and allows a confident prospective diagnosis of PLCH in the appropriate clinical setting. In typical cases, a predominantly nodular pattern is seen on CT scans in early phases of the disease, whereas a cystic pattern predominates in later phases. The radiologic abnormalities may regress, resolve completely, become stable, or progress to advanced cystic changes. Treatment consists of smoking cessation, but corticosteroid therapy may be useful in selected patients. Chemotherapeutic agents and lung transplantation may be offered to patients with advanced disease. The prognosis of PLCH is variable with frequent regression, stabilization, or recurrence of disease that does not correlate with cessation or continuation of smoking.

Genotypic analysis of pulmonary Langerhans cell histiocytosis

Reported studies show that the systemic form of Langerhans cell histiocytosis (LCH) is a clonal expansion of Langerhans cells (LC) associated with aberrant expression of several oncogenes or tumor-suppressor genes. LCH of the lung is a heterogenous group of lesions thought to be a reactive rather than neoplastic process. The histogenesis of the LCH of the lung is uncertain, and to date there are no studies investigating its underlying molecular abnormalities. We performed comparative genotypic analysis by using allelic loss (LOH) of polymorphic microsatellite markers associated with tumor suppressor genes. Fourteen cases of formalin-fixed, paraffin-embedded LCH of the lung were studied. Microdissection of a total of 26 nodules from 14 patients and paired reference lung tissue was performed under stereomicroscopic visualization. To evaluate allelic loss, we used a panel of 11 polymorphic microsatellite markers that were situated at or near tumor suppressor genes on chromosomes 1p, 1q, 3p, 5p, 9p, 17p, and 22q. The PCR products were analyzed by using capillary electrophoresis to identify germline heterozygous alleles and LOH. Allelic loss at 1 or more tumor suppressor gene loci was identified in 19 of 24 nodules. The total fractional allelic loss (FAL) ranged from 6% (1q) to 41% (22q), with a mean of 22%. The FAL in individual cases ranged from 0 (7 nodules) to 57% (1 nodule). Fifteen discordant allelic losses at 1 to 3 chromosomal loci were identified in 8 patients with multiple synchronous nodules. Our results show that LOH of tumor suppressor genes is present in the LCH of the lung, and they indicate that the putative tumor suppressor genes situated on chromosomes 9p and 22q may play a role in the development of a subset of the LCH of the lung.

[Adult pulmonary Langerhans' cell histiocytosis]

INTRODUCTION

Adult pulmonary Langerhans'cell histiocytosis, also referred to as histiocytosis X, is a disorder of unknown etiology which affects preferentially young smokers. The disease is characterized by granulomatous lesions which progressively invade and destroy distal airways, leading to the formation of characteristic cicatricial kystic lesions. Florid granulomas contain numerous Langerhans'cells, antigen-presenting cells of the dendritic cell lineage, associated with T lymphocytes and eosinophils. The diagnosis rests on the combination of clinical and radiologic data, and particularly on high-resolution CT scan findings showing a typical association of nodular and cystic changes, predominantly in the upper and middle lobes. Further evaluation with surgical lung biopsy is indicated in less typical situations.

CURRENT KNOWLEDGE AND KEY POINTS

The pathogenesis of Langerhans'cell histiocytosis is not fully understood, but several arguments suggest that the disease results from an abnormal immune reaction initiated by Langerhans'cells and directed against the bronchial epithelium. Other arguments suggest the presence of genetic abnormalities susceptible, for example, to increase the sensitivity of these cells to cytokines (GM-CSF, or others) known to influence their survival and maturation.

FUTURE PROSPECTS AND PROJECTS

These recent advances in the pathogenesis of Langerhans'cell histiocytosis could promote the development of new therapeutic strategies designed to regulate the number and activated state of Langerhans'cells in specific lesions.

Congenital self-healing langerhans cell histiocytosis with atrophic recovery of the skin: clinical correlation of an immunologic phenomenon

The pathophysiology and pathogenesis of congenital self-healing Langerhans cell histiocytosis (CSHLCH) as well as that of the other types of Langerhans cell histiocytosis is not well understood. Some authors postulate deregulated immunologic mechanisms that result in overproduction of cytokines. We examined a neonate with disseminated papulonodular eruptions containing lymphoid aggregates of B lymphocytes in the chorial layer. The diagnosis of a CSHLCH was made and the follow-up showed a complete involution of the eruptions, leaving atrophic lesions in the sites corresponding to the initial findings. We discuss a possible imbalance of the immune response as a pathogenetic mechanism.

Severe pulmonary hypertension in histiocytosis X

Diminished exercise capacity in advanced pulmonary histiocytosis X does not appear to be related to ventilatory limitation but may be related to pulmonary vascular dysfunction. Pulmonary hemodynamics and respiratory function were studied in 21 consecutive patients with advanced pulmonary histiocytosis X, and compared with parameters of patients with other severe chronic lung diseases (29 patients with chronic obstructive pulmonary disease and 14 patients with idiopathic pulmonary fibrosis). All patients with pulmonary histiocytosis X displayed severe pulmonary hypertension: mean pulmonary arterial pressure, 59 +/- 4 mm Hg; cardiac index, 2.6 +/- 0.8 L/min/m(2); and total vascular pulmonary resistance, 25 +/- 3 IU/m(2) (p < 0.05, as compared with patients with other chronic lung diseases). Pa(O(2)) was similar in the three groups, whereas FEV(1) was lower in patients with other chronic lung diseases (p < 0.05). In contrast to other chronic lung diseases, the degree of pulmonary hypertension was not related to variables of pulmonary function in pulmonary histiocytosis X. Histopathology was available for 12 patients with pulmonary histiocytosis X and revealed proliferative vasculopathy involving muscular arteries and veins, with prominent venular involvement. Two consecutive lung samples (taken before and after the occurrence of pulmonary hypertension) were available for six patients with pulmonary histiocytosis X, and showed that pulmonary vasculopathy worsened, whereas parenchymal and bronchiolar lesions remained relatively unchanged. These results indicate that pulmonary hypertension in pulmonary histiocytosis X might be related to an intrinsic pulmonary vascular disease, in which the pulmonary circulation is involved independent of small airway and lung parenchyma injury.

Evidence That Langerhans Cells in Adult Pulmonary Langerhans Cell Histiocytosis Are Mature Dendritic Cells: Importance of the Cytokine Microenvironment

Because Langerhans cells (LC) in peripheral tissues are generally “immature” cells with poor lymphostimulatory activity, the contribution of immune responses initiated by LC to the pathogenesis of pulmonary LC histiocytosis (LCH) has been uncertain. In this study we demonstrate that LC accumulating in LCH granulomas are phenotypically similar to mature lymphostimulatory dendritic cells present in lymphoid organs. LC in LCH granulomas intensely expressed B7-1 and B7-2 molecules, whereas normal pulmonary LC and LC accumulating in other pathologic lung disorders did not express these costimulatory molecules. The presence of B7+ LC in LCH granulomas was associated with the expression in these lesions, but not at other sites in the lung, of a unique profile of cytokines (presence of GM-CSF, TNF-α, and IL-1β and the absence of IL-10) that is known to promote the in vitro differentiation of LC into cells expressing a lymphostimulatory phenotype. Finally, LCH granulomas were the only site where CD154-positive T cells could be identified in close contact with LC intensely expressing CD40 Ags. Taken together, these results strongly support the idea that an abnormal immune response initiated by LC may participate in the pathogenesis of pulmonary LCH, and suggest that therapeutic strategies aimed at modifying the lymphostimulatory phenotype of LC may be useful in the treatment of this disorder.

Role of granulocyte-macrophage colony stimulating factor (GM-CSF) in the pathogenesis of adult pulmonary histiocytosis X

BACKGROUND

Pulmonary histiocytosis X is a disorder characterised by the presence of destructive granulomas preferentially involving distal bronchioles, that contain numerous activated Langerhans' cells. Recent studies have shown that granulocyte-macrophage colony stimulating factor (GM-CSF), which is produced by normal bronchiolar epithelium, may play an important part in the distribution and differentiation of Langerhans' cells. The aim of this study was to evaluate the role of this factor in the pathogenesis of pulmonary histiocytosis X.

METHODS

Four patients with pulmonary histiocytosis X were examined by immunohistochemical techniques for GM-CSF and CD1a surface molecules.

RESULTS

In early lesions the epithelium of bronchioles affected by the disease was strongly positive for GM-CSF and infiltrated by numerous CD1a+ Langerhans' cells organised into granulomas. In contrast, the expression of GM-CSF was substantially lower in bronchioles not affected by the disease, and these bronchioles contained few Langerhans' cells. When destruction by histiocytosis X lesions was more advanced, only remnants of bronchiolar epithelium could occasionally be identified; these remained strongly reactive for GM-CSF. Langerhans' cells within granulomas also moderately expressed this cytokine.

CONCLUSIONS

These results support the hypothesis that GM-CSF could be one of the factors responsible for the local accumulation of lymphostimulatory Langerhans' cells in early lesions of pulmonary histiocytosis X.

The dendritic cell lineage: a ubiquitous antigen-presenting organization

Dendritic cells are specialized antigen-presenting cells with two unique characteristics: the greatest stimulatory potential and the ability to stimulate naive T-lymphocytes. They originate from the bone marrow and reach their destination via hematogenous or lymphatic migration. Their phenotype is characterized by a high expression of major histocompatibility complex class II molecules and a high expression of adhesion molecules (CD25, CD54, CD58, CD72, and CD80). Pulmonary dendritic cells may be investigated by histologic examination, phenotype analysis, and function studies in a mixed lymphocyte reaction. Their isolation requires enzymatic digestion of lung tissue and subsequent steps of cell separation. The complexity of these manipulations makes it difficult to obtain large numbers of viable cells. A close anatomic relationship with alveolar macrophages underlines a functional interconnection: macrophages down-regulate the antigen-presenting function through release of tumor necrosis factor alpha. Dendritic cells most probably play a major role in lung diseases such as histiocytosis, primary and secondary cancers, and both acute and chronic lung graft rejection. Identification of the precise functional pathways might lead to therapeutic use of modulation of dendritic cell function.

Tobacco smoke induced lung granulomas and tumors: association with pulmonary Langerhans cells

The density of zinc-iodide-osmium (ZIO) positive pulmonary Langerhans dendritic cells (LC) was increased about 20-fold in mice after passive exposure to tobacco smoke. This was associated with pulmonary changes consistent with the cigarette smoking-related clinical syndrome in humans, pulmonary Langerhans cell granulomatosis. The major feature was an interstitial peribronchial granuloma. The cellular infiltrate of the granuloma (lymphocytes, plasma cells, eosinophils, clusters of large histiocyte-like cells and macrophages) extended into the adjacent alveolar septum forming a star-shaped lesion. The histiocyte-like cells were large with pale acidophilic cytoplasm and many ill-defined short dendrites extending from the cell membrane. Bronchial epithelial metaplasia also developed. The interstitial changes were followed by the development of proliferative alveolar and bronchial lesions in 2 mice. The zinc-iodide-osmium positive cells were consistent with la positive pulmonary dendritic cells and their ultrastructure was similar to that of pulmonary Langerhans cells. After ceasing exposure to tobacco smoke the density of pulmonary Langerhans cells returned to that of the control level; interstitial granulomatous lesions disappeared, but the bronchial epithelial metaplasia did not reverse. Tobacco smoke exposure of mice produces interstitial granulomatous inflammation similar to Langerhans cell granulomatosis in humans. The elevated level of pulmonary Langerhans cells implicate these cells in the pathogenesis of these lesions.

Modulation of fibroblast activity in histiocytosis X by platelet-derived growth factor

Platelet-derived growth factor (PDGF) was shown to modulate fibroblast activity in interstitial lung diseases like idiopathic pulmonary fibrosis (IPF). The role of PDGF in fibrosing mechanisms in histiocytosis X is unclear. Eight patients with histiocytosis X, five patients with idiopathic pulmonary fibrosis (IPF), and nine patients with no evidence of interstitial lung disease underwent bronchoalveolar lavage (BAL). The c-sis gene (a proto-oncogen encoding for the B-chain of PDGF) expression was measured by gene hybridization revealing an upregulated c-sis transcript in the group of histiocytosis X and patients, whereas no c-sis expression was detectable in the control group. The alveolar macrophage supernatants from histiocytosis X patients and from the control group were incubated with a human lung fibroblast cell line (WI-38). The mitosis rate was measured by tritiated thymidine incorporation and collagen production was estimated by determining the procollagen III peptide concentration in fibroblast supernatants. Tritiated thymidine uptake was increased 1.6 times in histiocytosis X compared with the control group (p < 0.01). Procollagen-III-peptide levels in fibroblast supernatants after incubation with alveolar macrophage supernatants from histiocytosis X were elevated 2.5 times compared with the control group (p < 0.01). Prior to incubation with the WI-38 cell line, the cell supernatant then was preincubated with nonpreserved anti-human PDGF (AA- and BB-chain) resulting in an 80% decrease of tritiated thymidine uptake and procollagen-III-peptide production in the group of histiocytosis X patients compared with native supernatants. No significant change in fibroblast activity was seen in the control group. Preincubation with nonpreservated Ki-T2 antibodies as pan T-lymphocyte marker did not show significant differences in both groups excluding unspecific antibody inhibition. These findings suggest increased PDGF production by alveolar macrophages in histiocytosis X patients. The PDGF is in part responsible for increased fibroblast replication and collagen production.

Langerhans' cell histiocytosis cells are activated Langerhans' cells

Langerhans' cell histiocytosis (LCH) is characterized by the presence of large mononucleated cells, associated with inflammatory cells. The Langerhans' cell (LC) lineage of the mononucleated cells is suggested by the presence of Birbeck granules and the expression of CD1a. We investigated the presence of 14 markers expressed by normal LCs in vitro. Nine skin and one lymph node frozen biopsies of LCH children were analysed by in situ immunohistochemistry. The data were compared with six skin and five lymph node frozen biopsies. LCH cells of the ten samples were positive for all 14 LC markers. We observed three different groups of markers, according to the respective staining of normal LCs and LCH cells. Group 1 included DR, DQ, CD1a, CD1c, and ICAM-3. Markers of group 1 were present on the majority of both normal LCs and LCH cells. Group 2 included CD1b, CD4, LFA-1, LFA-3, CD32, and CD68. Markers of group 2 were detected on the majority of LCH cells, but only on a fraction of normal LCs. Group 3 included CD11b, CD24, and B7/BB1. Markers of this group were detected on LCH cells, but not on normal LCs. This in situ immunohistochemical study confirms that LCH cells belong to the LC lineage. The different clinical LCH syndromes had the same immunohistochemical staining. The expression of some markers of groups 2 and 3 is known to be related to the activation of LCs in vitro. Our study suggests that LCH cells are activated LCs.