Polarization colours of collagen fibres: a sign of collagen production activity in fibrotic processes.

The maturation process of collagen fibres was investigated by the picro-sirius red/polarization light technique in experimental wound healing, in allyl-alcohol induced subacute and chronic liver fibrosis and in human biopsy material. Evidence was obtained that collagen fibres undergo a rapid maturation in fibrotic processes; the intensity of their birefringence increases and, at the same time, their polarization colour changes. Newly formed collagen fibres appear on the 4-6 mum thick sections in green polarization colour. Later, in a more mature stage, they became yellow, orange or red under crossed polaroids. The findings suggest that the simple picro-sirius red/polarizing light technique may be useful to form an opinion about the activity of the fibrotic process.