Human Tissue-Resident Mucosal-Associated Invariant T (MAIT) Cells in Renal Fibrosis and CKD.

BACKGROUND: Mucosal-associated invariant T (MAIT) cells represent a specialized lymphocyte population associated with chronic inflammatory disorders. Little is known, however, about MAIT cells in diseases of the kidney, including CKD. METHODS: To evaluate MAIT cells in human native kidneys with tubulointerstitial fibrosis, the hallmark of CKD, we used multicolor flow cytometry to identify, enumerate, and phenotype such cells from human kidney tissue biopsy samples, and immunofluorescence microscopy to localize these cells. We cocultured MAIT cells and human primary proximal tubular epithelial cells (PTECs) under hypoxic (1% oxygen) conditions to enable examination of mechanistic tubulointerstitial interactions. RESULTS: We identified MAIT cells (CD3+ TCR Vα7.2+ CD161hi) in healthy and diseased kidney tissues, detecting expression of tissue-resident markers (CD103/CD69) on MAIT cells in both states. Tissue samples from kidneys with tubulointerstitial fibrosis had significantly elevated numbers of MAIT cells compared with either nonfibrotic samples from diseased kidneys or tissue samples from healthy kidneys. Furthermore, CD69 expression levels, also an established marker of lymphocyte activation, were significantly increased on MAIT cells from fibrotic tissue samples. Immunofluorescent analyses of fibrotic kidney tissue identified MAIT cells accumulating adjacent to PTECs. Notably, MAIT cells activated in the presence of human PTECs under hypoxic conditions (modeling the fibrotic microenvironment) displayed significantly upregulated expression of CD69 and cytotoxic molecules perforin and granzyme B; we also observed a corresponding significant increase in PTEC necrosis in these cocultures. CONCLUSIONS: Our findings indicate that human tissue-resident MAIT cells in the kidney may contribute to the fibrotic process of CKD via complex interactions with PTECs.

Interferon-γ production by tubulointerstitial human CD56bright natural killer cells contributes to renal fibrosis and chronic kidney disease progression.

Natural killer (NK) cells are a population of lymphoid cells that play a significant role in mediating innate immune responses. Studies in mice suggest a pathological role for NK cells in models of kidney disease. In this study, we characterized the NK cell subsets present in native kidneys of patients with tubulointerstitial fibrosis, the pathological hallmark of chronic kidney disease. Significantly higher numbers of total NK cells (CD3-CD56+) were detected in renal biopsies with tubulointerstitial fibrosis compared with diseased biopsies without fibrosis and healthy kidney tissue using multi-color flow cytometry. At a subset level, both the CD56dim NK cell subset and particularly the CD56bright NK cell subset were elevated in fibrotic kidney tissue. However, only CD56bright NK cells significantly correlated with the loss of kidney function. Expression of the tissue-retention and -activation molecule CD69 on CD56bright NK cells was significantly increased in fibrotic biopsy specimens compared with non-fibrotic kidney tissue, indicative of a pathogenic phenotype. Further flow cytometric phenotyping revealed selective co-expression of activating receptor CD335 (NKp46) and differentiation marker CD117 (c-kit) on CD56bright NK cells. Multi-color immunofluorescent staining of fibrotic kidney tissue localized the accumulation of NK cells within the tubulointerstitium, with CD56bright NK cells (NKp46+ CD117+) identified as the source of pro-inflammatory cytokine interferon-γ within the NK cell compartment. Thus, activated interferon-γ-producing CD56bright NK cells are positioned to play a key role in the fibrotic process and progression to chronic kidney disease.

Cross-Reactivity to Mutated Viral Immune Targets Can Influence CD8+ T Cell Functionality: An Alternative Viral Adaptation Strategy.

Loss of T cell immunogenicity due to mutations in virally encoded epitopes is a well-described adaptation strategy to limit host anti-viral immunity. Another described, but less understood, adaptation strategy involves the selection of mutations within epitopes that retain immune recognition, suggesting a benefit for the virus despite continued immune pressure (termed non-classical adaptation). To understand this adaptation strategy, we utilized a single cell transcriptomic approach to identify features of the HIV-specific CD8+ T cell responses targeting non-adapted (NAE) and adapted (AE) forms of epitopes containing a non-classical adaptation. T cell receptor (TCR) repertoire and transcriptome were obtained from antigen-specific CD8+ T cells of chronic (n=7) and acute (n=4) HIV-infected subjects identified by either HLA class I tetramers or upregulation of activation markers following peptide stimulation. CD8+ T cells were predominantly dual tetramer+, confirming a large proportion of cross-reactive TCR clonotypes capable of recognizing the NAE and AE form. However, single-reactive CD8+ T cells were identified in acute HIV-infected subjects only, providing the potential for the selection of T cell clones over time. The transcriptomic profile of CD8+ T cells was dependent on the autologous virus: subjects whose virus encoded the NAE form of the epitope (and who transitioned to the AE form at a later timepoint) exhibited an 'effective' immune response, as indicated by expression of transcripts associated with polyfunctionality, cytotoxicity and apoptosis (largely driven by the genes GZMB, IFNÉ£, CCL3, CCL4 and CCL5). These data suggest that viral adaptation at a single amino acid residue can provide an alternative strategy for viral survival by modulating the transcriptome of CD8+ T cells and potentially selecting for less effective T cell clones from the acute to chronic phase.

Specialized Roles of Human Natural Killer Cell Subsets in Kidney Transplant Rejection.

Background: Human natural killer (NK) cells are key functional players in kidney transplant rejection. However, the respective contributions of the two functionally distinct human NK cell subsets (CD56bright cytokine-producing vs. CD56dim cytotoxic effector) in episodes of allograft rejection remain uncertain, with current immunohistochemical methods unable to differentiate these discrete populations. We report the outcomes of an innovative multi-color flow cytometric-based approach to unequivocally define and evaluate NK cell subsets in human kidney allograft rejection. Methods: We extracted renal lymphocytes from human kidney transplant biopsies. NK cell subsets were identified, enumerated, and phenotyped by multi-color flow cytometry. Dissociation supernatants were harvested and levels of soluble proteins were determined using a multiplex bead-based assay. Results were correlated with the histopathological patterns in biopsies-no rejection, borderline cellular rejection, T cell-mediated rejection (TCMR), and antibody-mediated rejection (AMR). Results: Absolute numbers of only CD56bright NK cells were significantly elevated in TCMR biopsies. In contrast, both CD56bright and CD56dim NK cell numbers were significantly increased in biopsies with histopathological evidence of AMR. Notably, expression of the activation marker CD69 was only significantly elevated on CD56dim NK cells in AMR biopsies compared with no rejection biopsies, indicative of a pathogenic phenotype for this cytotoxic NK cell subset. In line with this, we detected significantly elevated levels of cytotoxic effector molecules (perforin, granzyme A, and granulysin) in the dissociation supernatants of biopsies with a histopathological pattern of AMR. Conclusions: Our results indicate that human NK cell subsets are differentially recruited and activated during distinct types of rejection, suggestive of specialized functional roles.

Identification and Quantitation of Leukocyte Populations in Human Kidney Tissue by Multi-parameter Flow Cytometry.

Inflammatory immune cells play direct pathological roles in cases of acute kidney injury (AKI) and chronic kidney disease (CKD). However, the identification and characterization of distinct populations of leukocytes in human kidney biopsies have been confounded by the limitations of immunohistochemical (IHC)-based techniques used to detect them. This methodology is not amenable to the combinations of multiple markers necessary to unequivocally define discrete immune cell populations. We have developed a multi-parameter, flow cytometric-based approach that addresses the need for panels of cell-specific markers in the identification of immune cell populations, allowing both the accurate detection and quantitation of leukocyte subpopulations from a single, clinical kidney biopsy specimen. In this approach, fresh human kidney tissue is dissociated into a single cell suspension followed by antibody-labeling and flow cytometric-based acquisition and analysis. This novel technique provides a major step forward in identifying and enumerating immune cell subpopulations in human kidney disease and is a powerful platform to complement traditional histopathological examinations of clinical kidney biopsies.