An ELISA technique for quantification of surfactant apoprotein (SP)-C in bronchoalveolar lavage fluid

Am J Respir Crit Care Med. 2002 Feb 15;165(4):470-4. doi: 10.1164/ajrccm.165.4.2102080.


Pulmonary surfactant apoprotein C (SP-C) is a small, unique peptide that contributes to the reduction of alveolar surface tension. Due to the extreme hydrophobic nature of this peptide it was hitherto not possible to quantify SP-C in biological samples by immunological techniques. Using a newly developed polyclonal antibody raised against recombinant human SP-C in rabbits, we now describe an enzyme-linked immunosorbent assay (ELISA) to quantitate SP-C in bronchoalveolar lavage fluid (BALF). Solid phase binding of the hydrophobic SP-C was achieved by transfer of the standard or BALF samples (diluted in 80% isopropanol, pH 3.5) to polystyrene microtiter plates. Sequential treatment with trifluoroethanol and methanol (2x) was employed to improve antigen presentation and to minimize the influence of phospholipids. With this assay, SP-C from human, rabbit, porcine, and bovine surfactant was detectable. No cross-reactivity of the antibody to human SP-A and monomeric and dimeric SP-B was encountered. Total serum proteins did not affect ELISA signals, as evident from spiking experiments. The detection limit of the ELISA ranged below 3 ng/ml, and intra- and interassay coefficients of variation were 3.5% (n = 16) and 5.3% (n = 6), respectively. Serial dilutions of BALF showed good linearity, and excellent recovery rates were obtained upon spiking of human BALF. A mean value of 579.5 +/- 45.9 ng/ml (mean +/- SEM) SP-C was found in BALF samples of human healthy volunteers (n = 22), corresponding to 26.61 +/- 1.91 microg SP-C/mg total phospholipids (PL). SP-C levels were significantly lower in BALF of patients with acute respiratory distress syndrome (ARDS) (286.9 +/- 19.8 ng/ml [p < 0.001]; 13.92 +/- 1.93 microg SP-C/mg PL [p < 0.001], n = 48). We conclude that SP-C may be quantified with high specificity, reproducibility, and sensitivity in bronchoalveolar lavage samples by the presently described ELISA technique and that SP-C levels are significantly decreased in ARDS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoproteins / analysis*
  • Blotting, Western
  • Bronchoalveolar Lavage Fluid / chemistry*
  • Case-Control Studies
  • Enzyme-Linked Immunosorbent Assay / methods*
  • Humans
  • Pulmonary Surfactant-Associated Proteins*
  • Pulmonary Surfactants / analysis*
  • Reproducibility of Results
  • Respiratory Distress Syndrome / metabolism
  • Sensitivity and Specificity


  • Apoproteins
  • Pulmonary Surfactant-Associated Proteins
  • Pulmonary Surfactants
  • pulmonary surfactant apoprotein