Virtual crossmatching reveals upregulation of placental HLA-Class II in chronic histiocytic intervillositis

Abstract

Chronic histiocytic intervillositis (CHI) is a recurrent placental lesion where maternal macrophages infiltrate the intervillous space. Its cause is unknown, though due to similarities to rejected allografts one hypothesis is that CHI represents maternal-fetal rejection. Here, virtual crossmatching was applied to healthy pregnancies and those with a history of CHI. Anti-HLA antibodies, measured by Luminex, were present in slightly more controls than CHI (8/17 (47.1%) vs 5/14 (35.7%)), but there was no significant difference in levels of sensitisation or fetal specific antibodies. Quantification of immunohistochemical staining for HLA-Class II was increased in syncytiotrophoblast of placentas with CHI (Grade 0.44 [IQR 0.1-0.7]) compared to healthy controls (0.06 [IQR 0-0.2]) and subsequent pregnancies (0.13 [IQR 0-0.3]) (P = 0.0004). HLA-Class II expression was positively related both to the severity of CHI (r = 0.67) and C4d deposition (r = 0.48). There was no difference in overall C4d and HLA-Class I immunostaining. Though increased anti-HLA antibodies were not evident in CHI, increased expression of HLA-Class II at the maternal-fetal interface suggests that they may be relevant in its pathogenesis. Further investigation of antibodies immediately after diagnosis is warranted in a larger cohort of CHI cases to better understand the role of HLA in its pathophysiology.

Figure 1

Complement split product C4d in placental tissue and a kidney graft with confirmed antibody mediated rejection (AMR). (a) Healthy control placenta. (b) Index case of chronic histiocytic intervillositis (CHI). (c) Subsequent pregnancy following CHI diagnosis. d) A kidney biopsy with antibody mediated rejection (AMR). (e) Semi-quantitative grading of C4d staining. Bars represent median and error bars interquartile range. Statistical significance was tested using Kruskal–Wallis test. IVS intervillous space, V villi, Ve vessel. Arrows depict positive staining.

Figure 2

HLA expression in placenta. HLA-Class I immunohistochemical staining in (a) a healthy control placenta, (b) an index case of chronic histiocytic intervillositis (CHI) and (c) a subsequent pregnancy following diagnosis and treatment. HLA-Class II immunohistochemical staining is shown in (d) a healthy control placenta, (e) an index case of CHI and (f) a subsequent pregnancy. (f) IgG isotype control. HB Hofbauer cell, IVS intervillous space, M macrophage, V villus. Arrows depict positive staining.

Figure 3

Semi-quantitative grading of (a) HLA-Class I and (b) Class II expression in placentas from healthy control pregnancies, index cases of chronic histiocytic intervillositis (CHI) and subsequent pregnancies following diagnosis and treatment. Bars represent median and error bars interquartile range. Statistical significance was assessed via Kruskal–Wallis test, with Dunn’s multiple comparisons where differences were found. (c) and (d) Relationship between CD68 + macrophage infiltration in index cases of CHI and HLA-Class II and C4d deposition as determined by Spearman’s rank and simple linear regression.

Figure 4

Anti-HLA antibodies in healthy control pregnancies and subsequent pregnancies of women with a previous diagnosis of chronic histiocytic intervillositis (CHI). (a) Frequency of anti-HLA antibody positivity determined via Luminex screening. (b) Percentage calculated reaction frequency (%cRF) of antibody-positive study participants. %cRF reflects the percentage of donors an individual would be likely to reject based on the general population. Bars represent median and error bars interquartile range. (c) Class I Anti-HLA (HLA-A, B and C) antibody positivity. (d) Class II Anti-HLA (HLA-DP, DQ, DR) antibody positivity. e) %cRF values of antibody-positive participants versus placental intervillous C4d staining.

Figure 5

Fetal-specific anti-HLA antibodies (FSAs) in healthy control pregnancies and subsequent pregnancies of women with a previous diagnosis of chronic histiocytic intervillositis (CHI). (a) Number of FSAs determined via Luminex screening to identify antibodies towards paternally inherited HLA. (b) Mean fluorescence intensity (MFI) of individual FSAs. (c) Total MFI of FSAs for each participant. Bars represent median and error bars interquartile range.