FIG. 3.

K8.1ΔTMFc binds on the surface of mouse L cells (A) but not on the gro2C mutant (C) lacking heparan sulfate. Cells were fixed with paraformaldehyde and treated with Cohn fraction II derived from human plasma. Cells were then incubated with K8.1ΔTMFc (A, C, and E) or Fc alone (B, D, and F). Binding was detected with a mouse monoclonal antibody against the Myc epitope which was present at the C termini of both K8.1ΔTMFc and Fc, followed by incubation with a Cy3 labeled anti-mouse IgG antibody. Specific binding of K8.1ΔTMFc (A), but not of Fc alone (B), could be detected on mouse L cells. In contrast, K8.1ΔTMFc could not bind to the gro2C mutant of mouse L cells (22) lacking heparan sulfate expression (C and D). However, when cell line gro2C-EXT1, which is a derivative of gro2C with partially restored expression of heparan sulfate (28), was used, specific binding of K8.1ΔTMFc could again be observed (E and F).