Heterogeneity of type III procollagen N-terminal peptides in BAL fluid from normal and fibrotic lungs

Abstract

Levels of the N-terminal propeptide of type III collagen (PIIINP) in bronchoalveolar lavage fluid (BALF) are thought to reflect type III collagen production by the lungs, and increased levels have been reported in patients with pulmonary fibrosis. We wanted to know more about the relative proportions of these peptides in normal BALF, whether they altered in pulmonary fibrosis, and whether lymphoid tissue is capable of clearing PIIINPs. In this study, we used a radioimmunoassay which detects the different forms of PIIINP-related antigens with equal specificity, to measure PIIINPs in serum and BALF of patients with cryptogenic fibrosing alveolitis (CFA). To investigate why PIIINP profiles in BALF differed from serum, the absolute concentration and relative proportion of PIIINPs in lymph afferent and efferent to the popliteal lymph node of a sheep were also determined. PIIINP concentrations were significantly greater in serum and BALF of patients with CFA, compared with controls. Gel chromatography indicated that serum antigen distribution, both of patients and controls, contained approximately 20% Col 1-3; the remainder being Col 1. In contrast, BALF contained Col 1-3 and Col 1, together with an antigen of high molecular weight (> 150 kD). The relative proportion of each antigen varied quite widely, but there were no apparent differences between patients and controls. The concentration of PIIINPs in afferent lymph was 295 ng.ml-1 and in efferent lymph was 104 ng.ml-1. Gel chromatography demonstrated that a significant amount of Col 1-3, together with a high molecular weight peptide, had been cleared during passage through the node.(ABSTRACT TRUNCATED AT 250 WORDS)