CR2 and lymphoma: Because one of the possible causes of fever of unknown origin and lymphadenopathy is lymphoma (Burgueño and Abreu 2020), the flow cytometric assay for immunophenotyping with CD3-FITC (PC3/188A clone; Santa Cruz Biotechnology, Santa Cruz, CA, USA) and CD21-RPE (CA2.1D6 clone; Bio-Rad Laboratories, Hercules, CA, USA) was used to analyse samples obtained using fine-needle aspiration of superficial lymph nodes, indicating a heterogeneous population of lymphocytes (data not shown) that could eliminate lymphoma from the differential diagnosis list.