Table I.

Hemidesmosome Assembly in SCC12 Cells Maintained for 24 H on Various Matrices

Matrix		n of cells evaluated		Immature HDs		Immature HDs/100 microns		Mature HDs		Mature HDs/100 microns
pp126 cell ECM		19		34		12.72		3		1.12
pp126 cell ECM + plasmin		18		23		7.66		128		42.64
pp126 cell ECM + plasmin + 1947 mAb		19		33		13.5		24		9.82
Affinity-purified laminin-5		19		37		9.94		0		0
Affinity-purified laminin-5 + plasmin		20		23		6.24		53		14.38
Affinity-purified laminin-5 + plasmin + 1947 mAb		15		26		8.37		7		2.25

At 24 h after seeding onto the indicated matrices, SCC12 cells were processed for electron microscopy. Thin sections of the cells were prepared perpendicular to their substrate- attached surfaces. The numbers of mature and immature hemidesmosomes were evaluated over a known distance. In two series of studies, the matrix upon which the cells were plated was preincubated with the laminin-5 function-inhibiting antibody 1947. The greater number of hemidesmosomes assembled by SCC12 cells on plasmin-treated pp126 ECM versus plasmin-treated affinity-purified laminin-5 is most likely because there is more laminin-5 in cell-deposited matrix than can be captured by GB3 antibody onto a substrate. HD, hemidesmosome; ECM, extracellular matrix.