Mast cell distribution and density in the normal uterus--metachromatic staining using lectins

This study investigates the number and the distribution of mast cells in the normal human uterus. Reliability of results was ensured by prompt tissue fixation and the use of biotin-labelled lectins in conjunction with the avidin-biotin peroxidase complex (ABC) method. This design revealed that mast cells are, indeed, normal constituents of the human uterus. They occur in large numbers in the myometrium, but are only scanty in the endometrium where they tend to be confined to the stratum basalis. The mean mast cell counts per high power field (MC/HPF), after staining with Canavalia ensiformis agglutinin (Con A), were 17.9MC/HPF in the inner half of the myometrium, and 8.3MC/HPF in the outer half of the myometrium; 2.7MC/HPF in the basalis, and 0.3MC/HPF in the functionalis (P<0.05). There are no apparent differences in the number of mast cells between the normal proliferative and secretory phase endometrium, however, endometrial mast cells are considerably reduced and, apparently, depleted of metachromatic granules during the immediate pre-menstrual phase of the menstrual cycle. It is presumed that this, almost exclusive, presence of mast cells in the basal layer of the endometrial matrix, combined with the discharge of their cytoplasmic granules towards the end of the cycle, may be related with the contracting process preceding menstruation. On the other hand, the relative paucity of mast cells in the functional layer may contribute to the immune tolerance of the gestational endometrium to the implantation of the blastocyst.