Blood CD3-(CD56 or 16)+ natural killer cell distributions are heterogeneous in healthy adults and suppressed by azathioprine in patients with ANCA-associated vasculitides

Abstract

Background Cytotoxic Natural Killer (NK) cells are increasingly recognized as a powerful tool to induce targeted cell death in cancer and autoimmune diseases. Still, basic blood NK cell parameters are poorly defined. The aims of this study were 1) to establish reference values of NK cell counts and percentages in healthy adults; 2) to describe these parameters in the prototype autoimmune disease group ANCA-associated vasculitis (AAV); and 3) to investigate whether NK cell counts and percentages may be used as activity biomarkers in the care of AAV patients, as suggested by a preceding study. Methods CD3-(CD56 or 16)+ NK cell counts and percentages were determined in 120 healthy adults. Lymphocyte subset and clinical data from two German vasculitis centers were analyzed retrospectively (in total 407 measurements, including 201/49/157 measurements from 64/16/39 patients with granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), respectively). Results CD3-(CD56 or 16)+ NK cell counts and percentages in healthy adults were highly variable, not Gaussian distributed and independent of age and sex. NK cell percentages ranged from 1.9 to 37.9% of lymphocytes, and were significantly more dispersed in AAV (0.3 to 57.6%), while the median percentage was not different between AAV and healthy donors. In contrast, median NK cell counts were significantly lower in AAV compared to healthy donors. Sub-group analyses revealed that NK cell counts were low independent of AAV entity and disease activity. Azathioprine therapy was associated with significantly lower NK cell counts and percentages compared to non-azathioprine therapies. In 13.6% of azathioprine-treated patients, percentages were </= 1% which may be interpreted as temporary NK cell deficiency. NK cell counts and percentages could not separate active from inactive AAV. Conclusions NK cell counts and percentages in blood are heterogeneous and can presently not be recommended as biomarker in clinical care of AAV patients. Azathioprine treatment was associated with significantly low NK cells. These findings may be relevant for the development of drugs that aim at exploiting NK cell cytotoxicity and may help to identify patients at risk to develop malignant or infectious co-morbidities.

Natural Killer Cells in Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis - A Review of the Literature

“…Several publications describe unaltered NK cell numbers and percentages in peripheral blood mononuclear cells (PBMCs) of AAV patients compared to control ( Table 1 ) ( 52 , 54 , 58 , 59 ). The literature focusing on NK cell numbers or percentage in AAV is however inconclusive, and some studies instead report a decrease or increase of NK cell numbers or percentage in these patients ( 23 , 53 , 55 – 57 ), in line with what has been reported for some other autoimmune diseases ( 60 ). Also in healthy persons there is however great variations in percentage and absolute numbers of NK cells and high age is generally an important contributing factor that may vary between studies ( 23 ).…”

“…The literature focusing on NK cell numbers or percentage in AAV is however inconclusive, and some studies instead report a decrease or increase of NK cell numbers or percentage in these patients ( 23 , 53 , 55 – 57 ), in line with what has been reported for some other autoimmune diseases ( 60 ). Also in healthy persons there is however great variations in percentage and absolute numbers of NK cells and high age is generally an important contributing factor that may vary between studies ( 23 ). Hypothetically, this incongruence of data might also be explained by differences in the study population but also by the fact that the amount of NK cells in circulation can vary between AAV disease phenotype, different phases of the disease and in relation to treatment.…”

“…Variations in the phenotypic markers used to define NK cells in the different studies complicate comparisons. For example, older studies are limited by the identification of NK cells only with one phenotypic marker, often CD16, and in studies performed with clinical routine staining CD16 and CD56 are sometimes indistinguishable ( 23 ). The majority of NK cells in peripheral blood are CD56 dim , while CD56 bright NK cells are enriched in secondary lymphoid organs, such as lymph node or tonsil, and other tissue including liver ( 24 – 26 ).…”

“…Studies on how NK cells are affected by immunosuppressive treatment are scarce and there is no data if they can be used to predict relapses. Recently, low peripheral NK cell numbers and percentages in GPA and EGPA, but not MPA patients, were associated with azathioprine (AZA) treatment in a dose-dependent manner, but with no other investigated immunosuppressive treatments, including mycophenolate mofetil, methotrexate, RTX and CYC ( 23 ). The lack of effect of AZA treatment on the NK cells in the MPA group could be explained by the fact that MPA patients included in this study were older than the other AAV groups and age positively correlate with NK cell number.…”

NKG2D Natural Killer Cell Receptor—A Short Description and Potential Clinical Applications

“…Cells 2021, 10, 1420 2 of 24 cells express killer cell immunoglobulin-like receptors and have a strong cytolytic activity, whereas CD56bright cells secrete large quantities of cytokines [12][13][14][15]. The CD56dim cells make up to 90% of all blood NK cells, which makes them the major subset of NK cells, while CD56bright cells are present in lymphoid tissue [13].…”