Compartmental localization and clinical relevance of MICA antibodies after renal transplantation

Abstract

Background: Antibodies (Ab) responses to major and minor human leukocyte antigen loci may impact graft survival after organ transplantation.

Methods: A ProtoArray platform was used to study 37 serum samples from 15 renal transplant patients with (n=10) and without (n=5) acute rejection (AR) and seven normal controls, and the clinical relevance of major histocompatibility complex class I chain-related gene-A (MICA)-Ab measurements were investigated. Biopsy immunohistochemistry was conducted for localization of the MICA antigen.

Results: De novo MICA-Ab were detected in 11 of the 15 transplant patients in this study, irrespective of interval acute graft rejection. Mean MICA-Ab signal intensity was higher in transplant patients with C4d+AR (121.4) versus C4d-AR (4.3), correlated with donor-specific Ab to human leukocyte antigens (r=0.66, P=0.0078), was not elevated in cellular rejections, and correlated with decline in graft function over the subsequent year (r=0.73, P=0.0022). Integrative genomics accurately predicted localization of the MICA antigen to the glomerulus in the normal kidney (Li et al. Proc Natl Acad Sci USA 2009; 106: 4148), because this was confirmed subsequently by immunohistochemistry.

Conclusions: Integrative genomics analysis of ProtoArray data is a powerful tool to ascertain de novo antibody responses after renal transplantation and to accurately predict the anatomical location of the target renal antigens. This proof-of-concept study on MICA measurements by ProtoArray demonstrates that antibody responses modulated to MICA after transplantation in patients, irrespective of graft rejection, may be high at the time of humoral rejection and may not be elevated in cellular rejection. Understanding that MICA is preferentially localized to the glomerulus may explain both immunoregulatory and pathogenic roles for MICA after transplantation.

Fig 1. Work flow for identifying anti-MICA antibody

Work flow of study to identify compartmental localization and clinical relevance of MICA Antibodies by using integrated genomics approach.

Fig 2. Association between MICA immune response signal intensity and kidney chronic injury

A: Scatter plot for association between post-transplant sample time (months) and the signal intensity of MICA-Ab detected from ProtoArray from 15 patients, correlation coefficient = 0.03. B: Scatter plot for association between the change of calculated creatinine clearance by Schwartz equation over the subsequent year (Δ Crcl) and the signal intensity of MICA-Ab detected from ProtoArray from 15 patients, correlation coefficient = 0.73.

Fig 3. IHC staining on normal kidney, infiltrates, and cell types

Normal kidney: IHC staining for MICA-Ab on 7 compartments from normal kidney tissue. Cytoplasmic staining is observed solely in the glomerulus podocyte for MICA. AR kidney: The infiltrating mononuclear lymphocytes also showed strong positive staining for MICA in addition to positive staining in glomerular. Right upper corner: This biopsy is also seen to have focal staining of the peritubular capillaries (20%) and glomerular endothelial cells with C4d+. The lower panel shows the lymphocytic infiltrates in acute rejection: Dense lymphocytic infiltrates in rejection stain positive for MICA+ cells, CD56+ NK cells, CD8+ T cells and CD20+ B cells.