Mast cell and eosinophil distribution and activation in human endometrium throughout the menstrual cycle

Tryptase and chymase immunolocalization techniques have been used to examine the distribution, activation, and tryptase/chymase phenotype of mast cells (MCs) in 107 endometrial specimens that represented every day of the human menstrual cycle. MCs were identified in the endometrium in all stages of the menstrual cycle; similar MC numbers were observed for the functionalis, basalis, and muscularis. Extensive MC activation/degranulation, as judged by extracellular tryptase, was a common feature of the functionalis in specimens sampled just prior to and during menstruation. MC activation was also prominent in the functionalis at times coincident with recognized stromal edema. MCs of the functionalis did not contain chymase; all stained for tryptase and represent the MCT phenotype. By contrast, the basalis and muscularis showed a proportion of MCs containing both tryptase and chymase, MCTC. One important function for extracellular MC tryptase and chymase is their ability to activate precursor forms of the matrix metalloproteinases, enzymes recognized as instrumental in stromal degradation. Quantitative analysis of MC numbers, expressed relative to stromal cell numbers/mm2, indicated no major changes during the menstrual cycle, although changes in MC morphology, granule content, and activation/degranulation were recognized for specific stages. Eosinophils, detected with monoclonal antibodies EG1 and EG2, were absent from extravascular sites between Days 5 and 26 but showed local accumulations just prior to and during menstruation. Since MCs and eosinophils between them contain a variety of potent mediators, it seems likely that both cell types assume important functional roles in relation to tissue and vascular remodeling associated with endometrial physiology.