246. A new look at menstrual repair: the role of CD34⁺ cells and CD56⁺ uterine NK cells

Abstract

Endometrial regeneration occurs rapidly in a low estrogen environment without observable mitosis following menstruation. We have used a combination of hysteroscopy, scanning electron microscopy and immuno-histochemistry to re-examine this poorly understood process. Full thickness endometrial biopsies from 25 cycling women were used for immuno-histochemical analysis of the distribution of CD34⁺ and CD56⁺ cells.

Histological appearances show that immediately preceding menstruation, a small population of CD34⁺ stromal cells are located in the basalis but that their numbers increase dramatically following the onset of menstruation, becoming the dominant stromal cell type at this time. Mean surface stromal count during menstruation of CD34⁺ cells was 5847/mm² (n = 8) compared with pre-menstrual 108/mm² (n = 7). Conversely CD56⁺ uNK cells in the endometrial stroma were minimal in the proliferative phase, mean 228/mm² (n = 6) reaching a mean 2709/mm² (n = 7) immediately pre-menstrually. There is a significant inverse correlation (at 0.01 level (2-tailed)) between CD34⁺ cells and CD56⁺ uNK cells across the menstrual cycle. We present additional scanning electron microscope and histological images to support the hypothesis that uterine endometrial repair may occur via a blood borne supply of CD34⁺ stem cells which differentiate in to elements of the endometrium; surface epithelium, glandular epithelium and stromal uNK cells. This hypothesis has profound clinical implications for the mechanisms and management of common gynaecological conditions resulting from abnormal endometrial repair and is contrary to the current understanding that uterine endometrium is replaced from basal remnants.