Figure 1.

BPV1- and 2-infected fibroblasts lose contact inhibition and form aggregates. (A): non-infected equine primary fibroblasts (ArcA) in passage 3 (P3): the cells display the typical flat, elongated, spindle-shaped morphology of normal fibroblasts. (B): loss of contact inhibition in BPV1-infected equine fibroblasts in P3: cells begin to aggregate and pile up. C and D: BPV1- (C) and BPV2-infected equine fibroblasts (D) form dense three-dimensional cell aggregates consistent with tumor cell spheres. These events were documented by inverse phase-contrast microscopy (Axiovert 40 CFL, Zeiss, Jena, Germany) at 50× and 100× magnification.