Measurements of CD56+ cells in peripheral blood and endometrium by flow cytometry and immunohistochemical staining in situ

BACKGROUND CD56+ cells in peripheral blood or the endometrium may be increased in women with reproductive failure. However, the relationship between numbers of peripheral blood CD56+ and endometrial CD56+ cells is uncertain. The aim of this study was (i) to compare the numbers of CD56+ cells in peripheral blood and endometrium in samples taken simultaneously and (ii) to compare measurements by flow cytometry and immunohistochemistry of CD56+ cells in the same endometrial biopsy. METHOD Endometrial biopsies and blood were obtained from women with recurrent miscarriage (n= 25) on days LH+7–LH+9 of the cycle. The total number of CD56+, CD56+ CD16− and CD56+CD16+ cells in blood was measured by flow cytometry; the number of CD56+ cells in the endometrium was determined by immunohistochemistry. Endometrial samples were also obtained from fertile women (n= 20) and used to measure CD56+ and CD45+ cells, by both flow cytometry and immunostaining. RESULTS There was no correlation between the numbers of total CD56+, CD56+CD16− or CD56+CD16+ in peripheral blood and the number of endometrial CD56+ cells in the same women. In endometrium from fertile women, a significant correlation was found between the numbers of CD56+ cells measured by flow cytometry and immunohistochemistry (correlation= 0.497, P= 0.026, when expressed as % total cells; correlation= 0.570, P= 0.009 when expressed as % CD45+ cells). CONCLUSIONS Measurements of CD56+ cells in peripheral blood do not correlate with endometrial CD56+ cell numbers and therefore should not be extrapolated to events in the endometrium. In contrast, measurements of endometrial CD56+ cells by flow cytometry and immunostaining correlate well.