Fig. 3. Binding and deposition of soluble pre-lam5, but not lam6, promotes spreading of 3–/– MKs. (A) Soluble lam5 and lam6 in conditioned media of HFKs and JEBG keratinocytes were trapped onto plastic surfaces using immobilized Mabs, and analyzed for adhesion and spreading of 3–/– MKs. Control IgG does not trap any adhesive activity. Anti-lam 3 Mab P5H10 traps both lam5 and lam6; anti-lam 2, Mab B4-6 traps only lam5. Immobilized lam5 and 6 promoted adhesion, establishing that both are inherently adhesive if deposited on the substratum. (B) 3–/– MKs were attached to glass coverslips as round cells. The glass surface was blocked with BSA, and the cells were cultured with soluble lam5 in conditioned media from HFKs (a,c) or soluble lam6 in JEBG keratinocytes-conditioned media (b,d). After 24 hours the cells were fixed, permeabilized and immunostained for the human laminin 3 chain (P5H10, c and d). Representative phase images are shown in (a) and (b). Bars, 25 µm.