Adult-onset autoimmune neutropenia with antineutrophil antibodies to an unknown neutrophil-specific antigen analyzed by using five cell-lineage immunofluorescence test and reactivity against cell lines expressing human neutrophil antigens

Abstract

Autoimmune neutropenia (AIN) is a rare autoimmune disorder characterized by the presence of antineutrophil antibodies in the patient's blood, resulting in increased neutrophil destruction [1][2][3][4][5]. Herein, we report the case of a patient with adult-onset AIN harboring antineutrophil antibodies to an unknown neutrophil-specific antigen (or antigens). These antibodies were analyzed by using two newly developed assay methods: five cell-lineage immunofluorescence test (IFT) [6] and reactivity against a panel of cell lines expressing particular human neutrophil antigens (HNAs), named KY-cell lines [7,8].An 80-year-old Japanese man with a 4-year history of prostate cancer was referred to our hospital because of neutropenia. Three-and-a-half years earlier, his white blood cell and neutrophil counts were within the normal range; thereafter, the white blood cell count gradually decreased. Although the gonadotropin-releasing hormone analog he had been receiving for limiting the prostate cancer was discontinued, his neutropenia did not resolve. He was asymptomatic, in good general health, had no history of infection and autoimmune disorder, and had never received cytotoxic drugs. Blood tests revealed severe neutropenia (white blood count of 1880/lL, with an absolute neutrophil count of 230/lL), a normal hemoglobin level, and a normal platelet count. Tests for autoantibodies, including anti-Ro/ SSA antibody, antinuclear antibody, proteinase-3-antineutrophil cytoplasmic antibody (ANCA), and myeloperoxidase-ANCA, were negative, indicating the absence of Sjögren's syndrome, systemic lupus erythematosus, or an ANCA-associated disorder. A bone marrow smear showed normocellular marrow without abnormal or dysplastic cells, but a markedly decreased number of myelocytes and more mature myeloid cells than myelocytes, suggesting maturation arrest at the promyelocyte stage. Myeloblasts and promyelocytes, megakaryocytes, lymphocytes, and erythroid cells were normal.We analyzed the patient's serum for the presence of antineutrophil antibodies by using the five cell-lineage IFT [6], a modified granulocyte IFT (G-IFT) in which antibodies against neutrophils, monocytes, T cells, B cells, and platelets from healthy volunteers can be detected simultaneously with low background interference (Fig. 1). The HNA-1 allotypes of the volunteers were previously determined. We found immunoglobulin (Ig)G and IgM class antineutrophil antibodies in his serum. The antibodies reacted in a similar manner with HNA-1a-homozygous neutrophils, HNA-1a/HNA-1b-heterozygous neutrophils, and HNA-1b-homozygous neutrophils and did not react with the other cell lineages. Consequently, the diagnosis of AIN was confirmed.To elucidate the specificity of the antibodies, we examined their reactivity against gene-transfected panel cell lines (termed KY-cell lines) selectively expressing the molecules belonging to the HNA system (HNA-1a, -1b, -1c, -2a, -4a, -4b, -5a, and -5b) except HNA-3a, the gene of which was not identified until very recently, by flow cytometry [7,8]...

Neutrophil antibodies are clinically important

“…It can present a clinical and diagnostic challenge as many adult women invariably have alloantibodies to neutrophils; the patient's neutrophil count is often too low to make a definitive serological identification of a self‐reactive autoantibody. HNA specificity of the autoantibody is much rarer in adults .…”