The thickening of basement membrane in synovial capillaries in rheumatoid arthritis.

Synovial tissues from seven rheumatoid arthritis (RA) patients were used for the ultrastructural investigation of capillary cellular components and basement membranes (BM). Attention has been specially paid to the mechanism of BM thickening of the capillaries in the inflammatory sites. The capillary BM were multilamellated in the inflammatory sites. The multilamellation was characteristic not only in the BM surrounding the endothelial cells and pericytes but also in the BM between these two types of cells. Cell debris was frequently encountered between the multilamellated BM. The hyperplasia and various stages of degeneration of the endothelial cells were observed in these regions. Some endothelial cells were activated and occasionally located in capillaries containing degenerated endothelial cells. The high incidence of these findings indicates the following hypotheses. The accelerated rate of death and replenishment of capillary cellular components may play a role in BM thickening in the inflammatory sites of RA synovium. These cells may not only produce one layer of BM in their life-time but may also be activated to produce excessive amounts of BM components to make several layers.