The bronchial epithelium is the major barrier between the host and the provoking antigens in bronchial asthma. Recent studies have indicated that the epithelium is a truly stratified structure, with the superficial columnar cells depending on the underlying basal cells for anchorage. Only columnar cells are shed into bronchial lavage fluid. The epithelium is more fragile in asthma and more cells are lost in clusters. Desmosomes appear to be the major structural adhesion mechanism at the plane of cleavage between the columnar cells and the basal cells. The alpha 6- and beta 4-integrins, which contribute to hemidesmosomes and anchor cells to the underlying basement membrane, are expressed solely by basal cells. The apical aspects of the columnar cells are sealed by tight and intermediate junctions. There is constitutive expression of ICAM-1 and E-selectin in the vasculature of the bronchial mucosa, and ICAM is also present within the epithelium. These findings indicate that the bronchial epithelium is a complex structure that, as a mucosal surface, has constitutive expression of inflammatory cell adhesion molecules to serve normal leukocyte traffic.

The exchange of cross-talks between cells relies on soluble factors or direct cell-cell contact. Soluble factors increase the expression of cell surface molecules that activate adjacent cells by direct contact to produce cytokines. In the lung, dendritic cells are potent inducers of T-cell proliferation, and the interaction between the two leads to the production of high amounts of TNF alpha and TNF beta. Of the molecules involved in these biologic functions, LFA-3, CD11c, and the combination of beta 1 and beta 2 integrins are the most efficient. However, blocking TNF alpha or TNF beta production does not affect the alloreaction. The interaction between activated T cells and monocytes resulted in a large production of IL-1 beta. In this reaction, CD69, CD2, and the beta 2 integrins (CD11a, b, c, and CD18) and also other molecules such as a 25- to 35-kD glycoprotein play an important part. Finally, interaction between monocytes and fibroblasts leads to the production of large amounts of collagenase and PGE2 by fibroblasts. Cell-associated IL-1, particularly IL-1 alpha and membrane-bound TNF alpha, can also play a crucial role in the process of cell-cell interaction. This interaction may be controlled by inhibitors to IL-1 and TNF.

A multitude of glycoproteins expressed in cellular membranes have been identified by monoclonal antibodies. Besides mediating transient cell/cell contacts, these molecules unequivocally function as receptor structures capable of transmitting signals for cell growth and differentiation. They are the central determinators of local immune responses, and they allow an adjustment of the recirculating immunocompetent cells to their respective local microenvironments. Given that receptor/ligand interactions are characteristic of particular in vivo sites, knowledge of structural and functional features of adhesion receptors can provide new prospects for a more targeted clinical immune intervention.

The accumulation of leukocytes into tissues is a characteristic feature of inflammatory reactions. This process is triggered by chemical signals generated in a tissue in response to an inflammatory stimulus e.g., invading microbes, other foreign organisms, allergens, or damaged tissue cells. The mechanisms involved in neutrophil and eosinophil accumulation in vivo are complex and dependent on an initial interaction between the leukocytes and the microvascular endothelial cells. This response is regulated by the coordinated expression and/or activation of leukocyte and endothelial cell adhesion molecules. The precise mechanisms that control the selective accumulation of eosinophils, as opposed to neutrophils, in certain inflammatory reactions (e.g., in IgE-mediated allergic reactions) remain unclear. This may be explained partly by the generation of eosinophil-specific inflammatory mediators and activation of selective adhesion pathways such as the VLA-4/VCAM-1 interaction. Although the neutrophil and eosinophil have distinct roles in host defense, they have been implicated in the pathogenesis of a number of inflammatory disorders. Thus, a better understanding of the events mediating and regulating neutrophil and eosinophil accumulation in vivo will be of considerable value in the development of therapeutic strategies for inflammatory disease states.

Integrins are heterodimeric glycoproteins that mediate cell-to-matrix and some cell-to-cell interactions. Recent evidence underscores the important roles of these receptors in signaling machines that transduce positional information into complex changes in cell behavior. As such, integrins have been shown to play critical roles in cell growth, differentiation, and migration. Most cells express multiple members of this family, but the integrin repertoire of any given cell appears to be highly tissue- and cell-type-specific. We have used the homology-based polymerase chain reaction to identify known and novel integrin subunits in airway epithelial cells. With this technique we have identified three novel integrin subunits that participate in the formation of at least four novel integrin heterodimers. The best characterized of these, alpha v beta 6, is a receptor for the extracellular matrix protein fibronectin, and appears to be expressed only in terminally differentiated mucosal epithelial cells. The novel alpha subunit, alpha 9, forms a heterodimer with the known beta subunit, beta 1, in some epithelial cell lines. Elucidatation of the specific roles these receptors play in airway health and disease will likely provide unique insights into both the biology of integrins and the biology of the airway epithelium.

Several distinct cell adhesion molecule families have recently been identified and found to be important in the inflammatory response and for epithelial and endothelial homeostasis. The integrin family of adhesion molecules functions in both cell-matrix and cell-cell interactions, whereas the cadherins serve as important cell-cell receptors for maintenance of epithelial integrity. The leukocyte integrins, selectins, members of the immunoglobulin supergene family, and specific carbohydrates mediate adhesive interactions between leukocytes and endothelial cells. The mechanisms of leukocyte-epithelial adhesion are less well understood, but integrins and members of the immunoglobulin supergene family are also involved. The role of these molecules in pulmonary structure and inflammation is currently being actively explored. Further knowledge of these interactions, and the interplay of adhesion molecules, cytokines, and chemoattractants is likely to lead to novel therapeutic modalities in inflammatory diseases of the airway and lung parenchyma. In this overview, the families of adhesion molecules will be summarized, and their relevance for pulmonary structure and inflammation will be discussed.

T-lymphocytes with T-cell antigen receptor (TCR) comprising a gamma chain and a delta chain (gamma delta+ T cells) are believed to be involved in the immune reaction to mycobacterial antigens, and they have been found in increased proportions in sarcoid patients. We evaluated the proportions of gamma delta+ T-lymphocytes and of two major gamma delta+ subpopulations, the V delta 1+ and the V delta 2+ T-cell subsets, in 10 normal blood donors, in 15 patients with tuberculosis (TB), seven of whom had pleural effusion (PE), and in 12 patients with pulmonary sarcoidosis (PS), nine of whom underwent bronchoalveolar lavage (BAL). T-cell subsets were evaluated in peripheral blood (PBL) of all subjects and in PE from patients with TB and in BAL from patients with PS. Compared with normal blood donors, patients with TB had increased proportions of PBL CD3+ gamma delta+ T cells (6 +/- 1% versus 14 +/- 3% of CD3+ T cells, p < 0.05) because of the presence of four patients who had an increase (respectively, 18.3, 22.0, 24.2, and 35.4% of CD3+ T cells) of gamma delta+ T cells. In patients with TB and PE, gamma delta+ T cells were 7.9 +/- 2.7%, a value not different from that in the tubercular PBL and in normal PBL. Although patients with PS had proportions of PBL gamma delta+ T cells (9.2 +/- 3.4%) similar to those in normal PBL, two patients had increased (35 and 31%) PBL gamma delta+ T-lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent studies suggest that cytokines such as recombinant interferon-gamma (rIFN-gamma) may play a role in the treatment of certain respiratory conditions associated with infection and inflammation. This study was designed to determine if rIFN-gamma could be delivered effectively in a group of normal human volunteers. The effectiveness of the inhaled delivery system was demonstrated by the recovery of free IFN-gamma in bronchoalveolar lavage (BAL) fluid and macrophage (M phi) expression of IP-10, an IFN-gamma-inducible molecule, after therapy but not at baseline. IL-1 beta, but not IL-8, gene transcripts also showed evidence for up-regulation after rIFN-gamma therapy. Compared with baseline, inhaled rIFN-gamma did not significantly alter clinical symptom scores, spirometry, morning peak expiratory flow rate (PEFR), or the response to methacholine. Of interest, the evening PEFR increased significantly (p = 0.02), from 568 +/- 36 L/min at baseline to 584 +/- 33 L/min after inhaled rIFN-gamma. Although there was no significant change in total white cell count in BAL fluid, the cellular composition did demonstrate a significant decrease in percentage of alveolar M phi (p = 0.02) and an increase in percentage of lymphocytes (p = 0.02) after rIFN-gamma. There were no histologic differences seen in bronchial biopsy specimens, and there was no evidence for up-regulation of ICAM-1 or HLA-DR expression after rIFN-gamma. We conclude that, in normal persons, rIFN-gamma can be effectively delivered by inhalation. Future trials using inhaled rIFN-gamma appear to be warranted for certain pulmonary diseases.

A common side effect of radiotherapy is the development of fibrosis in the irradiated tissue. To study the mechanisms of this fibrogenic response, we developed a model system of whole-lung radiation in the rat and studied the evolution of injury by assessment of the cells and protein recovered by lavage. Once the pattern of injury was known, we attempted to modulate this reaction by administering the cytokine interferon-gamma (IFN-gamma). Rats received 15 Gy radiation to the whole thorax and were studied by lung lavage at intervals of 1 to 35 days after radiation. The effect of radiation was an initial (24 h) leak of protein, unaccompanied by cellular alterations, that resolved by 48 h. This was followed 2 wk later by a phase of inflammatory cell recruitment and more significant protein leak. A third phase of increase in inflammatory cells and further increase in protein flux was noted at Day 35. A significant cellular infiltrate was seen in lung sections obtained from animals treated in parallel experiments. IFN-gamma was given by osmotic pump from Day 0 to Day 35. This treatment significantly attenuated the PMN recruitment and protein leak (p < 0.002 and 0.01, respectively) at Days 25 and 35. Histologic sections demonstrated reduced alveolar cellularity and exudate at Day 25 (p < 0.05); however, significant numbers of inflammatory cells and exudate were present in irradiated and IFN-gamma-treated animals at Day 35. These data indicate that inflammatory cell recruitment may play a role in the lung injury following radiation. Furthermore, these preliminary data indicate that a cytokine blocks this reaction.

The potential role of neutrophil elastase in exacerbating pulmonary infection and tissue damage in cystic fibrosis (CF) has led to proposals for treatment of lung disease in CF with the elastase inhibitor, alpha 1-proteinase inhibitor (alpha 1PI). Reports that alpha 1PI is inactivated in the CF lung suggest that the effectiveness of alpha 1PI therapy depends on the quantity of elastase present and the extent of alpha 1PI inactivation, both of which are expected to vary with disease severity. In this study we assessed the elastase-alpha 1PI profile in sputum and plasma from CF patients with various degrees of pulmonary involvement. Levels of active elastase in sputum samples increased with severity of pulmonary disease (F ratio = 5.63, p < 0.01), as did sputum levels of alpha 1PI (F ratio = 4.88, p < 0.01). A positive correlation was observed between sputum levels of active elastase and alpha 1PI (r = 0.68, p < 0.005). Plasma alpha 1PI levels were also elevated in CF patients compared with control subjects (p < 0.005), indicating a compensatory increase in plasma and sputum levels of alpha 1PI in response to increased elastase load. Molar levels of total immunogenic neutrophil elastase were, on average, 12 times higher than alpha 1PI in CF sputum. These results suggest that the major contributor to the elevated levels of active elastase observed in the CF lung is an increase in elastase release rather than inactivation of alpha 1PI.

Positive end-expiratory pressure (PEEP) commonly decreases cardiac output. The major cause of this is believed to be decreased venous return due to increased right atrial pressure. We hypothesized that when the lungs were hyperinflated they could also restrict venous return by directly compressing the thoracic vena cavae. We measured the longitudinal distribution of pressure in the thoracic vena cavae of 10 dogs on and off 10 mm Hg PEEP, in the supine (S), prone (P), right lateral (RL), and left lateral decubitus (LL) positions. In the superior vena cava (SVC) both on and off PEEP, and in the inferior vena cava (IVC) off PEEP, pressure fell uniformly from the thoracic inlet to the right atrium. However, in the IVC on PEEP, intravascular pressure fell abruptly by up to 5 mm Hg. This pressure drop occurred in a discrete (1 to 2-cm) segment of the IVC, suggesting a localized increased in extravascular surface pressure. When this pressure inflection was present, changes in right atrial pressure had no effect on pressure in the IVC upstream of the inflection, consistent with a "vascular waterfall." These observations were most prominent in the LL, least common in the RL, and variably present in the P and S positions. Occlusion of the right bronchus intermedius prior to PEEP (preventing right lower, middle, and accessory lobe inflation) prevented the appearance of the pressure inflection during PEEP in the LL but not in the S or P positions. We conclude that PEEP impedes venous return partly by direct compression of the IVC, predominantly in positions in which the IVC is non-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal studies and clinical pediatric practice have shown that acute alkalosis attenuates hypoxic pulmonary vasoconstriction (HPV). However, increased intracellular pH appears to enhance pulmonary vasoreactivity. We therefore hypothesized that prolonged alkalosis augments HPV. This study compares the effects of acute and prolonged alkalosis on HPV in isolated perfused lungs of 1-month-old lambs (n = 5) and the hypoxic responses of 300- to 500-microns diameter segments of pulmonary arteries (n = 7) from mature cats at control pH and after 30 min of alkalosis. In isolated lamb lungs, normocarbic (5% CO2) hypoxia (4% O2) increased the total pressure gradient (delta PT) by 6.0 +/- 2.7 (SEM) mm Hg (p < or = 0.05). Acute hypocarbia (3% CO2) increased the perfusate pH to approximately 7.52 and significantly decreased the hypoxic delta PT to normocarbic, normoxic (28% O2) levels. Subsequent exposure to normoxia (while maintaining alkalosis) further decreased delta PT. However, re-exposure to hypoxia after 60 min of normoxic alkalosis significantly increased delta PT by 11.6 +/- 1.6 mm Hg (p < or = 0.05) to a level similar to that seen during normocarbic hypoxia. The increased hypoxic reactivity (i.e., change in pressure between normoxia and hypoxia) during prolonged alkalosis was due to enhanced HPV of the small vessels within the middle segment of the pulmonary circuit, as defined by an inflow-outflow occlusion technique (p < or = 0.05). The occlusion data also suggested that most of this increase occurred in small arteries. Moreover, the hypoxic response of isolated small arteries from the cat was increased almost threefold (p < or = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial damage is a hallmark of acute lung injury. Endothelial mediators may increase pulmonary vascular tone and induce pulmonary arterial muscularization, thereby contributing to the pulmonary hypertension seen with acute lung injury. We measured plasma levels and net pulmonary clearance of endothelin-1, a potent endothelium-derived vasoconstrictor peptide and smooth muscle mitogen, in 26 patients with early acute lung injury, the adult respiratory distress syndrome, and pulmonary hypertension. Nineteen had another data collection at clinical improvement or worsening. Control subjects (n = 25) had no pulmonary hypertension or lung injury. Initial mixed venous and systemic arterial plasma endothelin-1 levels were elevated (4.6 +/- 0.6 SEM and 4.9 +/- 0.6 pg/ml, respectively) as compared with control subjects (0.9 +/- 0.1 and 0.6 +/- 0.1 pg/ml). The systemic arterial/venous endothelin-1 ratio was 1.1 +/- 0.1 (0.7 +/- 0.1 in control subjects), indicating a reduction in normal net pulmonary endothelin-1 clearance. With clinical improvement, as compared with clinical worsening, mean plasma endothelin-1 levels, arterial/venous ratio, and pulmonary arterial pressure fell significantly towards normal. Thus, patients with acute lung injury have marked early increases in circulating plasma endothelin-1 levels, associated with abnormal pulmonary endothelin-1 metabolism. These abnormalities reverse in patients who recover. Through its actions, endothelin-1 could contribute to the pulmonary hypertension seen in acute lung injury.