Human Herpes Virus 6 (HHV-6)-associated Lymphadenitis: Pitfalls in Diagnosis in Benign and Malignant Settings

Neutrophil and Eosinophil Extracellular Traps in Hodgkin Lymphoma

Classic Hodgkin lymphoma (cHL), nodular sclerosis (NS) subtype, is characterized by the presence of Hodgkin/Reed-Sternberg (HRS) cells in an inflammatory background containing neutrophils and/or eosinophils. Both types of granulocytes release extracellular traps (ETs), web-like DNA structures decorated with histones, enzymes, and coagulation factors that promote inflammation, thrombosis, and tumor growth. We investigated whether ETs from neutrophils (NETs) or eosinophils (EETs) are detected in cHL, and evaluated their association with fibrosis. We also studied expression of protease-activated receptor-2 (PAR-2) and phospho-extracellular signal-related kinase (p-ERK), potential targets/effectors of ETs-associated elastase, in HRS cells. Expression of tissue factor (TF) was evaluated, given the procoagulant properties of ETs. We analyzed 32 HL cases, subclassified as 12 NS, 5 mixed-cellularity, 5 lymphocyte-rich, 1 lymphocyte-depleted, 4 nodular lymphocyte-predominant HL (NLPHL), and 5 reactive nodes. Notably, a majority of NS cHL cases exhibited NET formation by immunohistochemistry for citrullinated histones, with 1 case revealing abundant EETs. All other cHL subtypes as well as NLPHL were negative. Immunofluorescence microscopy confirmed NETs with filamentous/delobulated morphology. Moreover, ETs formation correlates with concurrent fibrosis (r = 0.7999; 95% CI, 0.6192-0.9002; P ≤ 0.0001). Results also showed that HRS cells in NS cHL expressed PAR-2 with nuclear p-ERK staining, indicating a neoplastic or inflammatory phenotype. Remarkably, TF was consistently detected in the endothelium of NS cHL cases compared with other subtypes, in keeping with a procoagulant status. A picture emerges whereby the release of ETs and resultant immunothrombosis contribute to the inflammatory tumor microenvironment of NS cHL. This is the first description of NETs in cHL.

Immunodeficiency-Related Lymphoid Proliferations: New Insights With Relevance to Practice

PURPOSE OF REVIEW

Our understanding of risk factors and mechanisms underlying immunosuppression-related lymphoproliferative disorders continues to evolve. An increasing number of patients are living with altered immune status due to HIV, solid organ or hematopoietic stem cell transplant, treatment of autoimmune disease, or advanced age. This review covers advances in understanding, emerging trends, and revisions to diagnostic guidelines.

RECENT FINDINGS

The tumor microenvironment, including interactions between the host immune system and tumor cells, is of increasing interest in the setting of immunosuppression. While some forms of lymphoproliferative disease are associated with unique risk factors, common mechanisms are also emerging. Indolent forms, such as Epstein-Barr virus positive mucocutaneous ulcer, are important to recognize. As methods to modulate the immune system evolve, more data are needed to understand and minimize lymphoproliferative disease risk. A better understanding of individual risk factors and common mechanisms underlying immunosuppression-related lymphoproliferations will ultimately enable improved prevention and treatment of these disorders.