Am. J. Respir. Cell Mol. Biol., Vol 17, No. 1, Jul 1997, 84-90.
Distribution of receptors of collagen and globular domains of C1q in human lung fibroblasts
AS Narayanan, J Lurton and G Raghu
Department of Pathology, School of Medicine, University of Washington, Seattle 98195, USA.
Fibroblasts are the predominant cell type responsible for the synthesis of
collagen and other matrix elements in normal and fibrotic lungs. We have
previously reported that human lung fibroblasts are heterogeneous in C1q
binding and that subpopulations differing in C1q binding can be isolated
and subcultured. We have investigated the distribution of receptors for
C1q-collagen domain (cC1q-R) and globular domain (gC1q-R) in adult human
lung fibroblasts. Fibroblasts were isolated from cultures of adult human
lung explants in medium containing fresh- or heated plasma-derived human
sera and separated by FACS-cell sorting into populations binding to C1q
with high- (HF) and low- (LF) fluorescence. The cC1q-R was obtained from
fibroblast membrane preparations by affinity chromatography through an
anti-cC1q-R antibody column and its distribution was determined by Western
analysis. The presence of gC1q-R was determined by immunoblots using an
anti-gC1q-R antibody raised against a synthetic peptide. The results showed
that a 54 kD protein crossreacting with anti-cC1q-R antibody was produced
by LF cells, but it was barely detectable in HF cultures. Immunostaining
with anti-cC1q-R antibody revealed that most of the cells in LF cultures
were positive while the HF cells were negative. A 38 kD protein recognized
by anti-gC1q-R antibody was produced by lung fibroblasts; however, no
differences were detected in its distribution between LF and HF cultures.
SDS-polyacrylamide gel electrophoresis of membrane proteins binding to an
affinity column of C1q-globular fragment showed that the HF cultures
contain a approximately 51 kD protein, which was a minor component in LF
membranes. These data show that cC1q-R is expressed predominantly by a
population of human lung fibroblasts, while the 38 kD gC1q-R is produced by
all cells. Another 51 kD protein appears to be produced by a separate
population of fibroblasts which does not express cC1q-R. Our results
indicate that two lung fibroblast subtypes may be distinguished based on
production of the 54 kD putative cC1q-R and another 51 kD protein which
binds to C1q-globular domain.
