We first used the stored, endometrial biopsy specimens to compare the accuracy of plasma cell identification with MGP (as performed in the parent investigation) to the results obtained by immunostaining sections with antibodies specific for CD138 (syndecan-1). CD138 is a plasma cell-specific surface molecule that has been previously employed as an adjunct stain in the work-up of suspected cases of endometritis [3
]. As hypothesized, we detected a wide discrepancy between results reported for plasma cell identification with MGP and results obtained upon CD138 staining of the same endometrial specimens. In fact, 25% of cases originally diagnosed with endometritis had no detectable CD138+
cells (representative results shown in ), while CD138 immunostaining identified plasma cells in 35% of the cases originally diagnosed as normal endometrial tissue (representative results shown in and ). Using CD138 immunostaining as the new diagnostic gold standard, we found sensitivity and specificity of MGP for plasma cell identification to be 78% and 65%, respectively.
As prior reports suggest that infrequent detection of endometrial plasma cells may only nonspecifically identify upper genital tract inflammation (as opposed to being necessary and sufficient for endometritis diagnosis), we posited that stratification of endometritis into acute and chronic forms (as performed in the parent investigation using conventional histologic criteria) would not delineate endometrial inflammatory responses distinctive of either form. To test this hypothesis, we used a semi-quantitative immunohistochemical scoring system to compare the number of CD3, CD8, CD20, CD56, CD68, CD138, and MHC class II-positive cells from stored, endometrial biopsy specimens that had been diagnosed with acute or chronic endometritis to the numbers present among women identified with normal endometrial tissue. We observed that diagnosis of acute and chronic endometritis was associated with statistically significant increases in endometrial T cell, B cell, and plasma cell numbers compared to numbers detected in normal endometrial tissue (), suggesting that conventional histologic criteria correctly identified at least a subset of women with endometrial leukocytic infiltrates that were consistent with increased upper genital tract inflammation. Evaluation of the number of CD3, CD8, CD20, CD56, CD68, CD138, and MHC class II complex positive cells that were associated with acute or chronic endometritis, on the other hand, demonstrated endometrial leukocytic infiltrates nearly indistinguishable from one another ().
Fig. 2 Acute and chronic endometritis identified by conventional histologic criteria have indistinguishable leukocytic infiltrates. Stored endometrial biopsy sections identified as normal tissue or acute or chronic endometritis were immunostained for CD3, CD8, (more ...)
While the above findings suggested that a more accurate identification of endometrial plasma cells can be achieved via immunostaining of biopsy specimens with the plasma cell-specific surface molecule CD138 (), we had not fully addressed the possibility that isolated detection of endometrial plasma cells may be unreliable for diagnosis of chronic endometritis and, by extension, PID case definition. To best characterize the leukocyte subpopulations found among women at lower risk for PID development, we completed flow cytometric analyses on endometrial samplings from 10 women that had undergone elective hysterectomy for irregular vaginal bleeding. Similar to the results from previous immunohistochemically-based characterizations [12
], we detected CD45+
cells in all specimens that were consistent with macrophage and lymphocyte populations (). In addition, a distinct plasma cell population was present in 30% (3/10) of endometrial samples (). This latter finding corroborates earlier reports that used H&E/MGP stains to identify endometrial plasma cells among women at low risk for upper genital tract inflammation [1
]. It also provides an argument that even when highly accurate endometrial plasma cell identification is achieved, these cells represent only a nonspecific criterion for the diagnosis of histologic endometritis, if not interpreted in the context of additional indices of inflammation.
Fig. 3 Flow cytometric analysis of endometrial biopsies represents a powerful approach for identification of upper genital tract leukocytes (representative contour plots shown). After defining the CD45+ cell population (not shown), a large percentage was identified (more ...)