HISTOCHEMISTRY OF PLACENTA 



905 



chondria in the placental septa and basal 

 plate at full term indicate the presence of 

 large numbers of viable and functionally 

 active trophoblastic cells (Wislocki, 1951). 

 Very few of the trophoblasts appear to be 

 undergoing degeneration. 



Secondly, in normal human placentas de- 

 livered at full term, the basal plate is com- 

 posed predominantly of masses of cells 

 which are identifiable as trophoblasts by 

 cytologic and histochemical means (Wis- 

 locki, 1951). Only a few maternal decidual 

 cells which differ cytologically from tropho- 

 blasts are attached irregularly to the ma- 

 ternal surface of the expelled placenta. The 

 ground substance of the basal plate gives 

 an intense PAS reaction which seems to be 

 mainly attributable to fibrin (Figs. 15.49, 

 15.45, and 15.55) , and contains no acid phos- 

 phatase (Fig. 15.40) and only traces of alka- 

 line phosphatase (Fig. 15.42). In these re- 

 spects it differs completely from the matrix 

 of the decidua. However, after abnormal im- 

 plantation, culminating in the condition 

 termed placenta accreta, the basal plate and 

 septa {ilacenta are modified by the unusu- 

 ally deep penetration of the trophoblast into 

 the uterine wall, resulting in widespread in- 

 tercrescence of the fetal and maternal tissues 

 (Irving and Hertig, 1937) with obliteration 

 of the usually well defined demarcation of 

 the basal trophoblast from the decidua. 



4. Cytologic Comparisons of the Cytotro- 

 phoblasts with Decidual Cells 



The decidua, as revealed by histochem- 

 ical means, is composed mainly of rather 

 large cells exhibiting many reactions, some 

 of which distinguish them clearly from the 

 peripheral cytotrophoblasts. In the first 

 months of gestation both the trophoblasts 

 and the decidual cells contain large amounts 

 of glycogen which make it difficult to tell 

 them apart; as gestation advances glycogen 

 diminishes in both cell types, although a 

 considerable quantity persists in the decid- 

 ual cells until term. On the other hand, the 

 cytoplasm of the decidual cells does not 

 have the strong cytoplasmic basophilia 

 which characterizes the peripheral cyto- 

 trophoblasts. Furthermore, unlike the tro- 

 phoblasts, most of the decidual cells contain 

 droplets of neutral fat and give a strong 



reaction for acid phosphatase (Fig. 15.53) 

 (Wislocki and Dempsey, 1948). Also the 

 stippling observed in the trophoblasts fol- 

 lowing staining with PAS reagents after 

 exposure to saliva (Figs. 15.49 and 15.55) 

 is not seen in the decidual cells (Fig. 15.52) ; 

 instead they are stained a diffuse pink. Thus 

 certain features sharply differentiate the 

 two types of cells. 



In contrast to the ground substance of 

 the cytotrophoblastic cell columns, the ma- 

 trix of the decidua is characterized by the 

 presence of an argyrophilic collagenous re- 

 ticulum surrounding the decidual cells (Fig. 

 15.27). The matrix also contains an amor- 

 phous ground substance which stains meta- 

 chromatically with toluidin blue (Fig. 15.58) 

 and is quite deeply stained by PAS reagents 

 (Fig. 15.52). The metachromasia indicates 

 the presence in the matrix of an acid muco- 

 polysaccharide. These reactions characterize 

 the matrix throughout the entire period of 

 gestation, as has been demonstrated on 

 pieces of decidua vera and basalis obtained 

 at cesarian removal of human placentas at 

 full term (Wislocki, 1953). 



The basal plate of the delivered human 

 placenta exhibits, as a rule, a sharp line of 

 demarcation between a wide zone of tro- 

 phoblasts and fibrin and an incomplete, ir- 

 regularly narrow lamina of decidua at- 

 tached to its outer surface. The decidual 

 cells of this narrow strip or border, which 

 represents the "junctional" or "penetration" 

 zone, differ from those in the general bulk 

 of the decidua in that the cells are markedly 

 degenerated. This zone gives a strong enzy- 

 matic reaction for acid phosphatase (Figs. 

 15.40 and 15.53) and a faint, irregular, non- 

 enzymatic reaction by the method for alka- 

 line phosphatase, the latter attributable 

 mainly to the presence of calcium salts in 

 this region (Fig. 15.42) (Dempsey and Wis- 

 locki, 1946). 



5. Cytolytic and Proteolytic Activities 0/ 

 Peripheral Trophoblasts 



In the first weeks of gestation the cytotro- 

 phoblast of the trophoblastic shell seems to 

 produce proteolytic and cytolytic substances 

 capable of attacking the endometrium 

 (Wislocki and Bennett, 1943; Wislocki, 

 Dempsey and Fawcett, 1948). In the early 



