1. In order to address the hypothesis that migrating fibroblasts have a different phenotype, human fetal lung fibroblasts (HFL-1) cells were evaluated in the Boyden blindwell chamber migration assay followed by immunoelectron microscopy.

2. HFL-1 cells were placed on nucleopore filters and incubated for 2 h using purified human plasma fibronectin (pFn) as a chemoattractant. Filters were then processed for immunoelectron microscopy using antibodies for α-smooth muscle (α-SM) actin as a marker for myofibroblasts, cellular fibronectin (cFn) and VLA-5.

3. Cells which had migrated to the bottom side of the filter were more likely to express α-SM actin, 29.1 ± 3.4% of cells, compared with cells which did not migrate through the filter, 12.4 ± 1.3% (P < 0.05). The total proportion of α-SM-actin-positive cells located on both sides of the filter showed no difference between those which had migrated toward pFn and controls (17.7 ± 1.0% compared with 20.2 ± 2.5%).

4. cFn-positive cells showed minimal differences compared with control cells, while perinuclear and endoplasmic reticulum staining of VLA-5 was observed only in the cells treated with pFn.

5. The results show that HFL-1 cells are heterogenous for α-SM actin expression. Short-term incubation with pFn did not change the proportion of α-SM-actin-positive HFL-1 cells. Cells which migrate, however, are enriched for α-SM actin expression. pFn-induced fibroblast chemotaxis can selectively recruit myofibroblasts with increased α-SM actin expression, a feature which may contribute to the altered population of cells at sites of fibrosis.

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