Abstract
Impaired graft function in the postoperative course after lung transplantation (LTx) may in part be due to alterations in pulmonary surfactant. Animal data provide increasing evidence for surfactant abnormalities in the early course after graft reperfusion. However, little is known about the integrity of the surfactant system in human lung transplant recipients. We therefore investigated surfactant properties in bronchoalveolar lavage fluid (BALF) of patients with lung transplants (n = 60) in comparison to that of healthy subjects (n = 10). The phospholipid concentrations of BALF and of surfactant subfractions were measured, and total protein was analyzed. Surface activity was measured with a pulsating bubble surfactometer (PBS). Minimum surface tension was 15.8 ± 1.1 mN/m in lung transplant recipients, whereas healthy subjects had minimum surface tensions of 3.4 ± 1.9 mN/m (p = 0.0004). As a marker for potential surfactant inhibition, protein-to-phospholipid (PL) ratios showed no significant differences in the two major study groups. The ratio of small surfactant aggregates to large surfactant aggregates was increased in patients with lung transplants (p = 0.043). Episodes of infection or rejection did not change surface activities, nor did they induce altered ratios of protein to PL or of small to large surfactant aggregates. Surfactant activity did not correlate with pulmonary-function data. Moreover, surface tension showed no correlation with the time after transplantation. Our results suggest a persistent impairment of biophysical surfactant properties after LTx, possibly due to type-II-cell malfunction.
There is increasing evidence that the pulmonary surfactant system is altered after lung transplantation (LTx). Surfactant abnormalities have been demonstrated in animal models in studies of the effects of preservation and ischemia–reperfusion injury following LTx. Biochemical and biophysical alterations in surfactant occur early during conventional lung preservation when the pulmonary artery is flushed with preservative solution (1). Prolonged storage of donor lungs further impairs the integrity of the surfactant system, with alveolar accumulation of potential surfactant-inhibiting proteins. Surface activity is decreased, and changes in phospholipid (PL) composition and surfactant-specific proteins have been described (2, 3). These modifications result in impaired gas exchange. Moreover, exogenous surfactant treatment was shown to improve lung function after prolonged storage times in experimental LTx (4-8). Thus, it was speculated that surfactant treatment could minimize ischemic damage to pulmonary allografts and thus prolong ischemic times in pulmonary transplantation (9).
Data on pulmonary-surfactant function in bronchoalveolar lavage fluid (BALF) of human lung transplant recipients, especially over the long-term course after LTx, are not available. Therefore, the aim of our study was to investigate biophysical and biochemical surfactant properties in BALF of lung transplant recipients in comparison with healthy volunteers.
We studied 46 lung and heart–lung transplant recipients who received transplants at the Hannover Medical School (mean age: 37.6 ± 1.5 yr [mean ± SEM]; 29 male and 17 female; see Table 1 for graft type and underlying disease). Patients underwent bronchoscopy for a decline in their pulmonary function, for a clinically suspected episode of infection or rejection, or as a routine procedure postoperatively. In these 46 LTx patients, 60 bronchoalveolar lavage (BAL) procedures were performed 439 ± 73 d after transplantation (range: 3 to 2,210 d; median: 200 d). Among the 60 BAL procedures, nine BALF samples came from lung transplant patients during the first two postoperative weeks (event-free subgroup n = 4), 15 BALF samples were from patients at 2 wk to 3 mo after surgery (event-free subgroup n = 9), another 15 BALF samples came from patients at 3 mo to 1 yr postoperatively (event-free subgroup n = 5), and 21 BALF samples were taken more than 1 yr after transplantation (event-free subgroup n = 10). All lung transplant recipients were receiving triple-drug immunosuppression with cyclosporine, glucocorticoids, and azathioprine. Retransplant recipients received FK506 instead of cyclosporine.
| Graft Type | Underlying Disease | No. of Patients | No. of BALs | |||
|---|---|---|---|---|---|---|
| HLTx | Total | 9 | 13 | |||
| Eisenmenger's syndrome | 5 | 7 | ||||
| Pulmonary hypertension | 2 | 4 | ||||
| Emphysema with right heart failure | 1 | 1 | ||||
| Pulmonary atresia | 1 | 1 | ||||
| BLTx | Total | 21 | 24 | |||
| Cystic fibrosis | 13 | 15 | ||||
| Obstructive lung disease | 6 | 7 | ||||
| Pulmonary hypertension | 1 | 1 | ||||
| Histiocytosis X | 1 | 1 | ||||
| SLTx | Total | 16 | 23 | |||
| Pulmonary fibrosis | 14 | 20 | ||||
| Emphysema | 1 | 2 | ||||
| Congenital cystic lung | 1 | 1 | ||||
| Total | 46 | 60 |
Routine surveillance of our lung transplant recipients included daily at-home spirometry and measurement of body temperature. Patients were asked to report to the lung transplant center whenever they noticed fever or a persistent deterioration of pulmonary function test results of more than 10%. In our center, pulmonary function measurements were made according to the American Thoracic Society (ATS) standardization criteria (10). Routine and transplant-specific blood-test specimens were taken and analyzed as recently described elsewhere (11).
Lung transplant recipients were divided into subgroups corresponding to their clinical status at the time of the study (e.g., event-free, infection, rejection, other). Diagnosis was made independently by two investigators (J.H. and H.H.) according to BALF data for microbiology and virology; blood-test results; and retrospective analysis of clinical course, treatment, and outcome. Among the 60 BAL procedures performed, 28 samples were obtained from stable patients (event-free). Twelve BALF samples were classified as having come from patients with acute rejection, seven from patients with bacterial infection, five from patients diagnosed as having viral infection, and eight from patients with episodes of other/unknown disease.
Ten healthy volunteers (mean age: 25.5 ± 0.7 yr; five male and five female) served as the control group. They had normal pulmonary-function test results (FEV1 = 103 ± 3% predicted; range: 85 to 120% predicted) and no history of a pulmonary disorder. The controls were nonsmokers and were receiving no medication. The study was approved by the ethics commitee of Hannover Medical School, and informed consent was obtained in all cases.
Fourteen BALs could not be correlated with lung function data because patients were unable to undergo pulmonary function testing owing to their early postoperative status. As a possible marker for severity of lung function impairment, DROP-FEV1, as the loss of FEV1 in milliliters per day prior to BALF sampling, was defined and calculated for the remaining 46 BALF samples as:
| Equation 1 |
where “current FEV1” means FEV1 on the day of BAL, and “previous FEV1” is the last documented FEV1 prior to BALF sampling. Whenever applicable (patients with lung transplants > 3 mo after LTx), an individual best FEV1 was determined according to the standardization criteria of the International Society for Heart and Lung Transplantation, for comparability of pulmonary function data (33 patients/38 BALF) (12). As a marker for graft function, BOS-FEV1 was defined and calculated for the appropriate 38 BALF specimens as:
| Equation 2 |
BAL was performed in a segment/subsegment of the middle lobe through fiberoptic bronchoscopy. In recipients of left-single-lung grafts, BAL was done in the lingula. Warm saline in five aliquots of 20 ml each was instilled and gently removed by mechanical suction. The lavage fluid was pooled and the recovered volume recorded (“recovery”). Specimens of 5 ml were forwarded for microbiology, virology and cell differential counting. The remaining lavage fluid was filtered through sterile gauze and then centrifuged at 250 × g for 10 min to obtain a cell-free supernatant. This supernatant was then stored frozen at −28° C until further analysis.
Protein content of the cell-free BALF supernatant was measured according to the method described by Lowry and coworkers (13). For measurement of total phospholipid content (PLt), an aliquot of the cell-free supernatant was used. In addition, quantities of PL were measured after high-speed centrifugation (see the following discussion) in the large-surfactant-aggregate (LA) pellet (PLLA) and in the small-surfactant-aggregate (SA)-containing supernatant (PLSA). PLs were extracted with chloroform/methanol according to the method described by Bligh and Dyer (14). Lipid extracts were dried under nitrogen, and PL phosphorus content was measured according to Bartlett (15). Absorbance was read at 800 nm, and phosphorus concentrations were calculated from a standard curve ranging from 5 μg to 190 μg phosphorus. All experiments were performed in duplicate.
The cell-free BALF supernatant was centrifuged at 48,000 × g for 60 min at 4° C to pellet LA. The supernatant containing SA was removed. The LA pellet was then resuspended with Ringer's solution, on the assumption that LA sedimentation would carry approximately 50% of the total PL. An aliquot of this resuspension was again analyzed for its PL content and adjusted with Ringer's solution at 2 mg PL/ml for measurements in the pulsating bubble surfactometer (PBS). Ringer's solution (Ringer-Lösung DAB7 Braun; Braun Melsungen, Melsungen, Germany) contained Na+ at 147 mM, K+ at 4 mM, Ca2+ at 2.3 mM, and Cl− at 155.5 mM.
Surface activity of surfactant material was measured with a PBS (16). PBS experiments were performed at hypophase concentrations of 1 mg PL/ml and 2 mg PL/ml. Briefly, 40 μl of the resuspended LA pellet were injected into the bubble chamber with a microtiter pipette. Before bubble pulsation was begun, the material was allowed to stabilize for 5 min. PBS measurements were made with a cycle speed of 20 cycles/min for 5 min. Prior to bubble oscillation, PL adsorption (γads) was measured as the surface tension of the originated bubble after a period of 10 s. Minimum surface tension at minimum radius of the bubble after 5 min of pulsation was defined as γmin. Maximum surface tension at maximum radius was defined as γmax. All analog data were digitalized and recorded by computer.
Results are expressed as mean ± SEM. Differences in means between the major study groups (LTx patients and controls) were tested with the nonparametric Mann–Whitney U test. Diversity between mean values of LTx subgroups and controls was analyzed with the Kruskal– Wallis test, followed by the Mann–Whitney U test for individual comparison. Values of p < 0.05 were considered significant. Bonferroni's post hoc correction for multiple comparison was used consistently.
Recovery of BALF was statistically different in patients with lung transplants and healthy volunteers (69.9 ± 1.3 ml versus 81.2 ± 2.0 ml, respectively; p = 0.0011). However, recoveries of approximately 70 to 80% of the instilled volume represent at least normal values for BAL procedures (17). BALF protein concentration was slightly greater in patients with lung transplants than in healthy controls (p = 0.041; Table 2). Interestingly, BALF protein content in the event-free subgroup was similar to that in control subjects (Table 2). The percentages of neutrophils, lymphocytes, and eosinophils were significantly increased in transplant recipients, whereas alveolar macrophages (AM) were decreased. Cell differentials of BALF from the study groups are shown in Table 2.
| Protein (μg/ml ) | Phospholipids (μg/ml ) | Macrophages (%) | Lymphocytes (%) | Neutrophils (%) | Eosinophils (%) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Control (n = 10) | 122.5 ± 8.0 | 38.0 ± 2.7 | 90.0 ± 0.7 | 6.8 ± 0.9 | 3.3 ± 0.5 | 0 ± 0 | ||||||
| All LTx (n = 60) | 184.4 ± 15.2* | 43.3 ± 2.5 | 64.6 ± 2.3* | 16.5 ± 1.6* | 16.9 ± 2.2* | 1.9 ± 0.3* | ||||||
| Event-free (n = 28) | 150.4 ± 21.4 | 38.1 ± 3.0 | 70.7 ± 2.5* | 15.7 ± 2.3 | 12.0 ± 2.0* | 1.7 ± 0.5 | ||||||
| AR (n = 12) | 220.3 ± 43.3 | 44.1 ± 4.2 | 61.8 ± 5.8* | 17.2 ± 3.6 | 17.7 ± 5.6 | 2.1 ± 0.7 | ||||||
| BI (n = 7) | 161.7 ± 25.5 | 50.6 ± 9.5 | 51.4 ± 8.3 | 12.2 ± 1.8 | 34.4 ± 9.0* | 2.3 ± 0.3 | ||||||
| VI (n = 5) | 194.7 ± 21.3 | 52.1 ± 10.7 | 62.7 ± 6.3 | 23.5 ± 5.6 | 11.6 ± 3.3 | 2.2 ± 0.4 | ||||||
| Other (n = 8) | 254.6 ± 41.5* | 48.3 ± 8.7 | 48.0 ± 2.6 | 19.3 ± 9.5 | 30.7 ± 9.7 | 2.0 ± 1.2 |
Although BALF recovery was significantly different between the major study groups, PL concentrations in cell-free supernatants were not different in controls and patients with lung transplants (43.3 ± 2.5 μg/ml versus 38.0 ± 2.7 μg/ml, respectively, p = 0.546; Table 2). PL concentrations did not vary significantly among the transplant subgroups (p = 0.40; Table 2). The protein/PL ratios were not different for the different study groups (p = 0.39; Figure 1).
Fig. 1. Protein/PL ratio in BALF from healthy subjects (control: black bars; n = 10), patients with lung transplants (all LTx: white bars; n = 60, p = 0.36), and transplant subgroups, consisting of patients without infection or rejection (event-free: diagonally striped bars; n = 28, p = 0.80), recipients suffering acute rejection (AR: horizontally striped bars; n = 12, p = 0.51), patients with bacterial infection (BI: patterned bars; n = 7, p = 0.70), and patients with viral infection (VI: vertically striped bars; n = 5, p = 0.46). Values are given as means ± SEM. p Values are given in comparison with control.
[More] [Minimize]The ratios of SA to LA in the lavage samples from patients with lung transplants and controls are shown in Figure 2. The SA/LA ratio was significantly higher in the samples from transplant recipients than in those from healthy controls (p = 0.043). In most LTx subgroups the SA/LA ratio was increased (p = 0.08). However, particularly in patients with lung transplants who were neither experiencing infection or rejection (event-free), the SA/LA ratio was not different than that of controls (0.122 ± 0.020 versus 0.094 ± 0.021, respectively; p = 0.256).
Fig. 2. SA/LA ratio in BALF from healthy subjects (control: black bars; n = 10), patients with lung transplants (all LTx: white bars; n = 60, p = 0.043), and transplant subgroups (as in Figure 1), consisting of event-free (diagonally striped bars; n = 28, p = 0.256), acute rejection (AR: horizontally striped bars; n = 12, p = 0.034), bacterial infection (BI: patterned bars; n = 7, p = 0.019), and viral infection (VI: vertically striped bars; n = 5, p = 0.713). Values are given as means ± SEM. Values are given in comparison with control. For subgroup comparisons, a p value < 0.01 was considered significant at the 5% level.
[More] [Minimize]In patients with lung transplants, there was a significant impairment of biophysical surfactant properties as compared with those of healthy volunteers (Figure 3a). This was even more obvious when PBS experiments were conducted at a hypophase PL concentration of 2 mg/ml (Figure 3b). Surfactants from stable (event-free) transplant recipients also displayed significantly less surface activity than control surfactants (Figure 4). Furthermore, surfactant activity was markedly and significantly impaired in all transplant subgroups (Figure 4a). In the transplant study group, minimum surface tension showed no correlation with the time course (i.e., number of days) after transplantation (Figure 5). Importantly, surface activity also showed no correlation with the time course in event-free transplant patients (γmin versus days after transplantation: r = 0.14, p = 0.487). In addition, BALF protein levels and SA/LA ratios did not correlate with the postoperative time course, either in all transplant patients studied (protein: r = 0.07, p = 0.61; SA/LA ratio: r = 0.22, p = 0.12) or in the event-free subgroup (protein: r = 0.19, p = 0.35; SA/LA ratio: r = 0.15, p = 0.51). Table 3 shows γmin, BALF protein levels, and SA/LA ratio values according to the various postoperative intervals of examination (i.e., the first two postoperative weeks, between 2 wk and 3 mo after surgery, between 3 mo and 1 yr postoperatively, and beyond 1 yr after transplantation) in the event-free LTx subgroup.
Fig. 3. Biophysical surfactant properties at hypophase PL contentrations of: (a) 1 mg/ml and (b) 2 mg/ml in healthy subjects (black bars; n = 10) and patients with lung transplants (white bars; n = 60). Surface tension (mN/m) after a 10-s adsorption period (γads) and at minimum (γmin) and at maximum (γmax) bubble size after 5 min of film oscillation are shown. Values are given as means ± SEM. p Values are given in comparison with control.
[More] [Minimize]Fig. 4. Biophysical surfactant properties at hypophase PL contentrations of 2 mg/ml in healthy subjects (control: black bars; n = 10), in patients with lung transplants (all LTx: white bars; n = 60), and in the appropriate transplant subgroups, as in Figure 1: Event-free (diagonally striped bars; n = 28), acute rejection (AR: horizontally striped bars; n = 12), bacterial infection (BI: patterned bars; n = 7), and viral infection (VI: vertically striped bars; n = 5). Surface tensions (mN/m) after a 10-s adsorption period (γads, bottom panel ) and at minimum bubble size after 5 min of film oscillation (γmin, top panel ) are shown. Values are given as means ± SEM. Values are given in comparison with control. For subgroup comparisons, a p value < 0.01 was considered significant at the 5% level.
[More] [Minimize]Fig. 5. Correlation of minimum surface tension (γmin) with days of BALF sampling after transplantation. Correlation coefficient and p value are given.
[More] [Minimize]| γmin(mN/m) | Protein (μg/ml ) | SA/LA Ratio (%) | ||||
|---|---|---|---|---|---|---|
| Days 0–14 (n = 4) | 21.7 ± 0.2 | 291 ± 92 | 0.05 ± 0.02 | |||
| Days 15–90 (n = 9) | 14.3 ± 3.4 | 140 ± 24 | 0.11 ± 0.03 | |||
| Days 91–365 (n = 5) | 20.9 ± 0.3 | 152 ± 37 | 0.13 ± 0.06 | |||
| Days > 365 (n = 10) | 10.7 ± 3.7 | 95 ± 21 | 0.16 ± 0.13 | |||
| p Value | 0.206 | 0.101 | 0.201 |
In patients with lung transplants, changes in pulmonary function, defined earlier as DROP-FEV1 and BOS-FEV1, were correlated with cell differential counts and with parameters of biophysical surfactant function (γmin, γmax, γads) and biochemical surfactant data (protein, PLt, PLLA, PLSA, protein/PL ratio, SA/LA ratio). There was a significant correlation between DROP-FEV1 and protein (r = 0.76, p < 0.0001; Figure 6a), and between DROP-FEV1 and protein/PL ratio (r = 0.69, p < 0.0001; Figure 6b). No other such correlations were found in the remaining comparisons.
Fig. 6. For patients with lung transplants, the data for (a) protein and (b) protein/PL ratio (prot/PL ratio) were correlated with pulmonary function test results. DROP-FEV1 represents loss of FEV1 in milliliters per day prior to BALF sampling. Correlation coefficients and significance levels are given.
[More] [Minimize]Several groups have reported abnormalities of the pulmonary surfactant system following LTx in animal models (1-3, 18). Surfactant alterations were shown to depend on preservation (1, 19) and graft ischemia time (3, 18). These studies have all focused on early surfactant changes in experimental pulmonary transplantation. Human data, especially in the long-term course after LTx, are missing. In this study we addressed surfactant alterations in human lung transplant recipients over a wide time range after LTx.
Marked disturbances of biophysical surfactant properties were consistently observed in lung transplant recipients. Abnormalities of surfactant function were found independently from the time course after transplantation. Thus, impaired surface activity was obvious both in the early postoperative course and in the long term follow-up. In individual patients who underwent serial bronchoscopy after LTx, surfactant function did not recover in the further course (data not shown). BALF protein and the SA/LA ratio also showed no clear correlations with postoperative course. However, BALF protein levels were found to be increased in the first 2 wk after transplantation (Table 3).
Because patients with lung transplants often suffer from episodes of infection or rejection, we analyzed surfactant function in the appropriate subgroups. It turned out that surface activity was dramatically decreased even in patients without episodes of infection or rejection at the time of BAL (event-free subgroup). However, surface activity was found to be below 5 mN/m in a few patients in this subgroup (eight of 28 patients; Figure 5), suggesting that under certain unknown conditions, alveolar surfactant function seems to be preserved or restored. In the entire event-free subgroup there was no difference in either protein or ratios of protein to PL or SA to LA in comparison with healthy controls. Therefore, in these patients it seems unlikely that protein inhibition of biophysical surfactant function, which is a well established mechanism in adult respiratory distress syndrome (ARDS) (20), played a major role. Moreover, the ratio of poorly functioning SA to superiorly functioning LA, which is thought to represent a marker of surfactant inactivation (21, 22), did not differ in event-free lung transplant patients and controls. Therefore, other mechanisms seem to account for the impaired surface activity in BALF in a group of patients with lung transplants.
One possible mechanism for such impaired surface activity is that changes in surfactant-specific proteins alter surfactant function. Surfactant-specific proteins, especially surfactant protein-B (SP-B) and probably SP-A and SP-C, enhance surface activity (23). In this respect, the important role of SP-B has recently been addressed (24). In a previous study we showed that SP-A is significantly decreased in patients with lung transplants as compared with controls (25). This could suggest that SP-A deficiency contributes to altered surfactant activity. Moreover, this preliminary finding of decreased SP-A levels after transplantation might reflect a type-II-cell malfunction. Further studies are needed to investigate the role of surfactant-specific proteins in disturbed surface activity after lung transplantation.
Another possible explanation for impaired surfactant function could be changes in PL composition. Dipalmitoyl-phosphatidylcholine (DPPC), the main PL fraction of surfactant with a major role in surface activity, was shown to be decreased in a canine single-lung transplantation model (2). Increases in sphingomyelin content and decreases in phosphatidylglycerol (PG) content were also demonstrated after experimental lung transplantation in the same species (3). Although the total PL concentration was found to be similar in patients with lung transplants and controls in our study, changes in PL composition, with a decrease of DPPC, might account for disturbed surfactant function following human LTx.
Impairment of biophysical surfactant properties did not correlate with pulmonary function data for lung transplant recipients. Neither graft function, expressed as BOS-FEV1 according to ISHLT criteria (12), nor current alteration of pulmonary function, expressed as DROP-FEV1, showed a significant correlation with surfactant function. Therefore, the role of pulmonary surfactant activity for graft function in the intermediate term after transplantation remains unclear. However, a significant correlation of DROP-FEV1 with protein content and with the protein/PL ratio was demonstrated. This may show that alveolar inflammation with protein influx has an impact on pulmonary function in patients with lung transplants. In this connection, not the causative disease itself (infection or rejection), but the resulting inflammatory process, with alveolar protein accumulation, seems to represent a parameter with which to anticipate pulmonary dysfunction.
Our results are the first to indicate that LTx not only disturbs surfactant function in the early postoperative stage, as shown in experimental LTx, but causes a persistent surfactant malfunction in lung transplant recipients. In the majority of these patients, the dimension of disturbed surface activity seems dramatic. The severity of biophysical surfactant changes in LTx is comparable to surfactant alterations in lung diseases with severe pulmonary dysfunction, like ARDS and severe pneumonia (20, 26). Minimum surface tensions of > 15 mN/m are assumed to result in marked loss of alveolar stability. In ARDS and pneumonia, signs of alveolar instability, such as alveolar and interstitial infiltrates, interstitial thickening, and impaired gas exchange are present. In contrast, our data show that in the majority of lung-transplanted patients, graft function in the long-term course is preserved despite disturbed surfactant function. In particular, no correlation of surface activity with graft function as defined by pulmonary function testing (BOS-FEV1) was found. Furthermore, transplant complications such as infection or rejection, which one would assume to be deleterious to surfactant function, did not further change surface activities in BALF of such patients in comparison with event-free subjects in our study. It is possible that ex vivo measurements of surface tensions in the bubble surfactometer do not reflect the in vivo condition precisely. In addition, as discussed earlier, the mechanisms of impaired surfactant function in LTx seem to differ from those in ARDS, (e.g., protein inhibition). Thus, besides our lack of information on the mechanisms responsible for disturbed surfactant function, we are far from answering the important question of the clinical relevance of surfactant abnormalities in lung transplant recipients. The role of pulmonary surfactant in the long-term after LTx has to be further elucidated, both experimentally and clinically. Therefore, it is essential to study differences in surfactant between the early postoperative period and later periods in greater detail and in a larger study population. Moreover, in future studies, different types of control groups should be used to identify the independent contributions of immunosuppressive therapy and thoracotomy to changes in surfactant function and composition. Therefore, surfactant alterations should be determined in liver or kidney transplant recipients being treated with the same immunosuppressive regimen as lung transplant recipients. In addition, it is important to analyze changes in endogenous surfactant in patients who undergo thoracotomy for nontransplant-requiring conditions.
Therapy with exogenous surfactant has been suggested to improve graft function and to prolong graft ischemia times in experimental LTx (4-8). In a patient with reperfusion edema, therapy with inhaled surfactant was shown to improve gas exchange and lung compliance (27). In the long-term course after transplantation, exogenous surfactant therapy by aerosol might be useful in patients with bronchiolitis obliterans syndrome (BOS). In this respect, the potential benefit of surfactant therapy in obstructive airways disease has recently been addressed (28). This innovative approach may be important all the more because present therapy for BOS is limited. Further studies to elucidate the possible role of exogenous surfactant therapy in patients with chronic allograft dysfunction are recommended.
The authors thank M. Heilmann, M. Klocke, W. H. T. Schürmann, H. Tschorn, and the technical staff of our bronchoscopy unit for their help in collecting BALF samples. The technical assistance of K. Balke and P. Erbe is greatly appreciated.
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