Reactive natural killer (NK) cells may show an altered immunophenotype under certain conditions, such as viral infections or in association with non‐NK cell hematopoietic neoplasms. Such conditions can result in the immunophenotype of reactive NK cells overlapping with that of neoplastic NK cells. Distinguishing reactive NK cell lymphocytosis with an altered immunophenotype from a neoplastic NK cell proliferation, especially chronic lymphoproliferative disorder of NK cells (CLPD‐NK), can be challenging. We report an unusual case of atypical reactive NK cell lymphocytosis in a chronic human immunodeficiency virus (HIV)‐infected patient presenting with anemia and persistent lymphocytosis.

The patient was a 63‐year‐old African American male with HIV infection/acquired immunodeficiency syndrome (HIV/AIDS) who presented with right‐side abdominal pain. His medical history was significant for chronic obstructive pulmonary disease, myelitis and arachnoiditis, hepatitis C, pulmonary tuberculosis, and prostate cancer status postirradiation. The patient had been HIV positive for more than 20 years; however, he started antiretroviral therapy only 1 year before this presentation. He had been previously hospitalized and treated for numerous infections. His complete blood count at presentation showed a leukocyte count of 7.36 × 10⁹/L with 59% (4.34 × 10⁹/L) lymphocytes, a hemoglobin level of 9.6 g/dL, and a platelet count of 221 × 10⁹/L. The peripheral blood smear showed increased large granular lymphocytes with bland nuclei, condensed chromatin, and moderate to abundant pale cytoplasm containing fine to coarse azurophilic granules (Figure 1a). Peripheral blood flow cytometry immunophenotyping showed increased NK cells (negative for surface CD3 and positive for CD56), accounting for 33% of the total mononuclear cells and 55% of the total lymphocytes. The NK cells were positive for CD2 and CD7, and negative for CD5. They showed heterogeneous expression of killer cell immunoglobulin‐like receptors (KIRs) CD158a, CD158b, and CD158e, and variable expression of CD8 and CD57. Notably, the NK cells showed atypical strong expression of CD94 and loss of expression of CD161 and CD16 (Figure 1b).

During the preceding 3 years the patient had poorly controlled HIV/AIDS with an absolute low CD4 count (106‐292/μl) and a chronic HIV viremia, ranging up to 23,200 copies/μl before antiretroviral therapy decreasing to 30–916 copies/μl after initiating therapy. The patient also had persistent absolute lymphocytosis (> = 4.0 × 10⁹/L) during the preceding 6 months. In conjunction with the clinical information and pathological features with heterogeneous KIR expression, a diagnosis of reactive NK cell lymphocytosis was favored. In addition, a subsequent bone marrow biopsy revealed an unremarkable bone marrow with rare NK cells, cytogenetic studies found a normal male karyotype, and peripheral blood STAT3 and STAT5b mutation analysis detected no mutations. These findings further support the reactive nature of the lymphocytosis rather than a neoplastic process. The patient was encouraged to follow up with the infectious disease and continue on antiretroviral medication.

This patient's atypical NK cell immunophenotype, in the context of persistent lymphocytosis and anemia, raised suspicion for CLPD‐NK. A comparison of the clinical and pathological features of the case presented here, CLPD‐NK, and normal NK cells is shown in Table 1 (Jevremovic & Olteanu, 2019; Swerdlow et al., 2017). CLPD‐NK is believed to have a phenotype distinct from that of normal NK cells. The immunophenotypic features of CLPD‐NK include abnormal expression of KIRs with either uniform expression of a single KIR or absence of all KIR antigens, bright/uniform CD94 expression, negative/dim CD56 expression, dim/heterogeneous CD161 expression, and positive CD16 expression. However, CLPD‐NK with positive CD56 and negative CD16 expression have also been reported. Moreover, approximately one‐third cases of CLPD‐NK show STAT3/STAT5b mutations. In comparison to CLPD‐NK, heterogeneous KIR expression and absence of STAT3/STAT5b mutation in the current case support the interpretation of the overall findings as a reactive polyclonal NK cell proliferation. Nevertheless, loss of both CD161 and CD16 expression and uniform, bright CD94 expression has not been reported in normal NK cell proliferations. In challenging cases such as this, an integrated diagnostic approach that utilizes clinical information, morphology, immunophenotyping, and molecular profiling is critical to make the correct diagnosis.

Reactive NK lymphocytosis with an altered immunophenotype has been reported in viral infections. Reduction of CD16 or diminished CD161 expression has been described in viremic HIV or HIV/CMV co‐infected individuals and is associated with NK cell function defects. In addition, increased expression of CD94 in T cells has been described in reactive states caused by primary Epstein–Barr virus infection. This case demonstrates that CD94 may also be overexpressed in reactive NK cells. Overall, the atypical NK cell immunophenotype in this case is likely associated with poorly controlled, chronic HIV infection.

In this study, we described an unusual case of reactive NK lymphocytosis with CD94 overexpression and loss of CD16 and CD161 expression in a patient with chronic HIV/AIDS. An integrated diagnostic approach was instrumental in making the diagnosis.

反应性自然杀伤 (NK) 细胞在某些条件下可能表现出改变的免疫表型，例如病毒感染或与非 NK 细胞造血肿瘤相关。这种情况会导致反应性 NK 细胞的免疫表型与肿瘤性 NK 细胞的免疫表型重叠。将免疫表型改变的反应性 NK 细胞淋巴细胞增多症与肿瘤性 NK 细胞增殖，尤其是 NK 细胞的慢性淋巴增生性疾病 (CLPD-NK) 区分开来可能具有挑战性。我们报告了一个慢性人类免疫缺陷病毒 (HIV) 感染患者出现非典型反应性 NK 细胞淋巴细胞增多症的罕见病例，该患者表现为贫血和持续性淋巴细胞增多症。

患者是一名 63 岁的非洲裔美国男性，患有 HIV 感染/获得性免疫缺陷综合征 (HIV/AIDS)，表现为右侧腹痛。他的病史在慢性阻塞性肺病、脊髓炎和蛛网膜炎、丙型肝炎、肺结核和放射后前列腺癌状态方面具有重要意义。患者 HIV 阳性已超过 20 年；然而，他在本次就诊前仅 1 年就开始了抗逆转录病毒治疗。他之前曾因多次感染住院并接受治疗。他就诊时的全血细胞计数显示白细胞计数为 7.36 × 10 ⁹ /L，其中淋巴细胞为 59% (4.34 × 10 ⁹ /L)，血红蛋白水平为 9.6 g/dL，血小板计数为 221 × 10 ⁹/L。外周血涂片显示大颗粒淋巴细胞增多，核温和，染色质凝聚，细胞质中至丰富，含有细至粗的嗜天青颗粒（图 1a）。外周血流式细胞术免疫表型显示NK细胞增多（表面CD3阴性，CD56阳性），占单核细胞总数的33%，淋巴细胞总数的55%。NK细胞对CD2和CD7呈阳性，对CD5呈阴性。他们表现出杀伤细胞免疫球蛋白样受体 (KIR) CD158a、CD158b 和 CD158e 的异质表达，以及 CD8 和 CD57 的可变表达。值得注意的是，NK 细胞表现出非典型的 CD94 强表达和 CD161 和 CD16 的表达缺失（图 1b）。

在过去的 3 年中，患者的 HIV/AIDS 控制不佳，CD4 计数绝对低 (106-292/μl) 和慢性 HIV 病毒血症，抗逆转录病毒治疗前高达 23,200 拷贝/μl，降至 30-916 拷贝/μl开始治疗后。该患者还具有持续的绝对淋巴细胞增多症 (> = 4.0 × 10 ⁹/L) 在过去 6 个月内。结合具有异质性 KIR 表达的临床信息和病理特征，反应性 NK 细胞淋巴细胞增多症的诊​​断是有利的。此外，随后的骨髓活检显示无明显异常的骨髓有罕见的NK细胞，细胞遗传学研究发现男性核型正常，外周血STAT3和STAT5b突变分析未检测到突变。这些发现进一步支持淋巴细胞增多的反应性质而不是肿瘤过程。鼓励患者跟进传染病并继续服用抗逆转录病毒药物。

该患者的非典型 NK 细胞免疫表型，在持续淋巴细胞增多和贫血的情况下，引起了对 CLPD-NK 的怀疑。此处介绍的病例、CLPD-NK 和正常 NK 细胞的临床和病理特征的比较如表 1 所示（Jevremovic & Olteanu，2019 年；Swerdlow 等人，2017 年））。CLPD-NK 被认为具有不同于正常 NK 细胞的表型。CLPD-NK 的免疫表型特征包括 KIR 的异常表达，具有单一 KIR 的均匀表达或所有 KIR 抗原的缺失、明亮/均匀的 CD94 表达、阴性/暗淡的 CD56 表达、暗淡/异质的 CD161 表达和阳性 CD16 表达。然而，也有报道 CD56 阳性而 CD16 表达阴性的 CLPD-NK。此外，大约三分之一的 CLPD-NK 病例显示 STAT3/STAT5b 突变。与 CLPD-NK 相比，当前病例中 KIR 表达的异质性和 STAT3/STAT5b 突变的缺失支持将总体发现解释为反应性多克隆 NK 细胞增殖。然而，CD161 和 CD16 表达和均一性的丧失，在正常 NK 细胞增殖中没有报道过明亮的 CD94 表达。在此类具有挑战性的病例中，利用临床信息、形态学、免疫表型和分子分析的综合诊断方法对于做出正确诊断至关重要。

在病毒感染中已经报道了具有改变的免疫表型的反应性 NK 淋巴细胞增多症。CD16 减少或 CD161 表达减少已在病毒血症 HIV 或 HIV/CMV 共感染个体中描述，并且与 NK 细胞功能缺陷有关。此外，在由原发性 Epstein-Barr 病毒感染引起的反应状态下，T 细胞中 CD94 的表达增加。该案例表明 CD94 也可能在反应性 NK 细胞中过度表达。总体而言，这种情况下的非典型 NK 细胞免疫表型可能与控制不佳的慢性 HIV 感染有关。

在这项研究中，我们描述了一个不寻常的病例，即慢性 HIV/AIDS 患者出现反应性 NK 淋巴细胞增多症，并伴有 CD94 过度表达和 CD16 和 CD161 表达缺失。综合诊断方法有助于诊断。