Pleural SC5b-9 in differential diagnosis of tuberculous, malignant, and other effusions

Soluble Membrane Attack Complex: Biochemistry and Immunobiology

The soluble membrane attack complex (sMAC, a.k.a., sC5b-9 or TCC) is generated on activation of complement and contains the complement proteins C5b, C6, C7, C8, C9 together with the regulatory proteins clusterin and/or vitronectin. sMAC is a member of the MACPF/cholesterol-dependent-cytolysin superfamily of pore-forming molecules that insert into lipid bilayers and disrupt cellular integrity and function. sMAC is a unique complement activation macromolecule as it is comprised of several different subunits. To date no complement-mediated function has been identified for sMAC. sMAC is present in blood and other body fluids under homeostatic conditions and there is abundant evidence documenting changes in sMAC levels during infection, autoimmune disease and trauma. Despite decades of scientific interest in sMAC, the mechanisms regulating its formation in healthy individuals and its biological functions in both health and disease remain poorly understood. Here, we review the structural differences between sMAC and its membrane counterpart, MAC, and examine sMAC immunobiology with respect to its presence in body fluids in health and disease. Finally, we discuss the diagnostic potential of sMAC for diagnostic and prognostic applications and potential utility as a companion diagnostic.

Tuberculous pleural effusion

Tuberculous pleural effusion (TBPE) is the most common form of extrapulmonary tuberculosis (TB) in Spain, and is one of the most frequent causes of pleural effusion. Although the incidence has steadily declined (4.8 cases/100,000population in 2009), the percentage of TBPE remains steady with respect to the total number of TB cases (14.3%-19.3%). Almost two thirds are men, more than 60% are aged between 15-44years, and it is more common in patients with human immunodeficiency virus. The pathogenesis is usually a delayed hypersensitivity reaction. Symptoms vary depending on the population (more acute in young people and more prolonged in the elderly). The effusion is almost invariably a unilateral exudate (according to Light's criteria), more often on the right side, and the tuberculin test is negative in one third of cases. There are limitations in making a definitive diagnosis, so various pleural fluid biomarkers have been used for this. The combination of adenosine deaminase and lymphocyte percentage may be useful in this respect. Treatment is the same as for any TB. The addition of corticosteroids is not advisable, and chest drainage could help to improve symptoms more rapidly in large effusions.

The use of non-routine pleural fluid analysis in the diagnosis of pleural effusion

The investigation of a pleural effusion is, in general, a very straight forward process with the combination of clinical history, examination, radiology and pleural fluid analysis leading to diagnosis in most cases. While most fluid samples are sent for routine analysis including protein, LDH, glucose, cytology and microbiology, there are a number of more unusual fluid analyses available which in some cases directly lead to, and in others are suggestive of the diagnosis. Moreover, other fluid markers are constantly being evaluated as a diagnostic tool. In this review, we describe these non-routine pleural fluid analyses in detail. English language publications in MEDLINE and references from relevant articles from January 1 1990 to August 1 2009 were reviewed. Keywords searched in combination were pleural fluid, effusion, analysis, transudate, exudate and diagnosis.

The use of adenosine deaminase and adenosine deaminase isoenzymes in the diagnosis of tuberculous pleuritis

The bacillary population described in tuberculous pleuritis is small, and its most likely pathogenetic mechanism is essentially immunologic. This explains why, until now, the diagnostic identification of tuberculous pleuritis (TP) has been based on the presence of granulomas in pleural biopsy. Correcting this diagnostic deficiency through other parameters related to the specific pathogenetic mechanism has been widely studied. The determination of the levels of adenosine deaminase (ADA) in pleural fluid offers high performance in its discriminating capacity to identify TP (sensitivity 87 to 100%, specificity 81 to 97%). Adenosine deaminase expresses the sum of two isoenzymes (ADA1 and ADA2). ADA1 is ubiquitous in all cells, including lymphocytes and monocytes, whereas ADA2 is found only in monocytes. Analysis and determination of these isoenzymes have shown that ADA in TP increases particularly at the expense of ADA2 and that the ADA1 /ADAp activity ratio improves performance in terms of sensitivity, specificity, and efficacy (100%, 92 to 97%, and 98%, respectively) in correcting all false-negative and false-positive results except 1 to 9% of nonlymphoproliferative malignancies. Only the high performance of ADA in the identification of TP allows it to be assumed that pleural biopsy can be obviated, especially in patients aged less than 35 years of age or having a lymphocyte-to-neutrophil proportion of more than 0.75 in regions of high prevalence. Quick determination and low cost justify its routine use in exudates. The ADA1 /ADAp activity ratio improves performance even more and could be used in cases with uncertain diagnoses or in regions with low prevalence of tuberculosis.

Sialyl stage-specific embryonic antigen-1: a useful marker for differentiating the etiology of pleural effusion

OBJECTIVES

To assess the usefulness of sialyl stage-specific embryonic antigen-1 (SSEA-1) levels in differentiating the etiology of pleural effusion (PE).

DESIGN

A solid-phase immunoradiometric sandwich assay with an FH6 monoclonal antibody was used to measure sialyl SSEA-1 levels in PEs of 132 patients with various diseases. Paired serum sialyl SSEA-1 levels were measured simultaneously in 47 patients with various subtypes of lung cancer

RESULTS

The pleural sialyl SSEA-1 levels were significantly higher in patients who had adenocarcinoma of the lung with positive cytology than in all the other patients, including those having malignancies other than adenocarcinoma of the lung, adenocarcinoma of the lung with cytology-negative PE, and benign diseases. There were no significant differences among sialyl SSEA-1 levels in the pleural fluid containing no adenocarcinoma cells. Using the cutoff value of 265 U/mL, the sensitivity was 64% (25/39) and the specificity was 95% (88/93) for the pleural sialyl SSEA-1 level to differentiate adenocarcinoma from other effusions.

CONCLUSIONS

With high specificity and modest sensitivity, the pleural sialyl SSEA-1 level is a useful biochemical marker for differentiating the etiology of PEs caused by adenocarcinoma from other diseases.

Complement components and their activation products in pleural fluid

STUDY OBJECTIVES

The aim of this study was to determine the role of complement components in pleural effusion measured with novel markers of complement activation, to assess which pathway of activation is predominant in different diseases, and to find out whether the analysis of complement components and their activation products could help in diagnostic procedure differentiating the etiologies of pleural effusion.

PATIENTS

The study population consisted of 71 patients who had pleural effusion secondary to tuberculosis (n=23), rheumatic disease (n=10), or malignancy (n=38).

MEASUREMENTS

Complement components and their activation products, including the soluble terminal complex SC5b-9, were measured in plasma and pleural fluid.

RESULTS

In all patients with rheumatic pleurisy, pleural fluid SC5b-9 was higher than 2 AU/mL and in all patients with malignant pleural fluid it was lower than 2 AU/mL. The mean level of SC5b-9 in rheumatic pleural effusion was also significantly higher than in tuberculosis. In addition, the concentrations of pleural fluid C3 and C4 were significantly lower and the ratio C4d/C4 was significantly higher in rheumatic compared with tuberculous or malignant pleurisy. In plasma, both SC5b-9 and C1s-C1r-C1INH-complexes were significantly higher in rheumatic subjects than in other patients. In stepwise multinominal logistic regression analyses, the most significant predictors for rheumatic pleural fluid were high pleural fluid SC5b-9 and low C4.

CONCLUSIONS

These observations indicate that the complement cascade is activated through both the classic and the alternative pathways in rheumatic pleurisy. Determinations of SC5b-9 and C4d/C4 in pleural fluid were the best variables differentiating rheumatic, tuberculous, and malignant effusions.

Diagnostic value of ferritin, haptoglobin, alpha 1-antitrypsin, lactate dehydrogenase and complement factors C3 and C4 in pleural effusion differentiation

Searching to define diagnostic criteria for malignant and non-malignant pleural effusions, the differential diagnostic value of ferritin (FRT), haptoglobin (Hp), alpha 1-antitrypsin (alpha 1-AT), lactate dehydrogenase (LDH) and complement factors C3 and C4 were investigated prospectively in 100 consecutive patients with pleural effusions of various aetiologies. Pleural effusion FRT, C3 and C4 concentrations were found to be useful in differentiating exudates from transudates, so that transudates practically could be excluded in pleural effusion: serum FRT ratio lower than 0.5 and/or in pleural effusion values for C3 and C4 higher than 300 mg dl-1 and 70 mg dl-1, respectively. A pleural effusion: serum C3 ratio greater than 2 is seen only in malignant effusions. No discriminative pleural: serum ratio could be found in FRT and C4 values capable of differentiating malignant from non-malignant effusions. Pleural effusion alpha 1-AT and LDH values were elevated in exudates, as compared with transudates, and had an excellent sensitivity and predictive value, but low specificity, in differentiating malignant from non-malignant effusions. Finally, the sensitivity, specificity and positive predictive value of pleural effusion Hp concentrations were lower than those of FRT and complement factors C3 and C4, respectively.