In order to assess the characteristics of its stromal cells and the di
stribution of extracellular matrix proteins, me investigated, immunohi
stochemically and ultrastructurally, term, first and second trimester
human umbilical cords. A differential distribution pattern of the vari
ous cytoskeletal proteins of stromal cells and extracellular matrix pr
oteins was observed in different zones of the stroma, the subamniotic
stroma, Wharton's jelly, and the vessels' adventitia. All three zones
showed immunoreactivities for collagen types I, III and VI and for bas
ement membrane molecules such as collagen type IV, laminin and heparan
sulphate proteoglycan. Immunoreactivities for these extracellular mat
rix molecules were observed around cleft-like territories (stromal cle
fts) in the Warton's jelly which were occupied by homogeneous ground s
ubstance but void of collagen fibrils and basal lamina molecules. More
over, between the stromal clefts, slender cells were found which immun
ohistochemically and ultrastructurally corresponded to various stages
of myofibroblastic differentiation. In earlier stages of gestation, st
romal cells with a less complex expression pattern prevailed. The stro
mal clefts and the contractile cells together might serve as a system
regulating the turgor of the cord. (C) 1997 W. B. Saunders Company Ltd
.