The pathogenesis of histiocytic necrotizing lymphadenitis (HNL), which was reported first by Kikuchi et al. and Fujimoto et al. in 1972, is as yet unknown. HNL is frequently reported in Asian countries including Japan, however it is rare in Europe and North America. To elucidate whether the human leukocyte antigen (HLA) alleles and haplotypes are associated with HNL, we performed DNA typing of HLA class II genes (HLA-DR, -DQ, and -DP) in 86 patients with HNL and 525 unrelated healthy Japanese controls with polymerase chain reaction using sequence-specific oligonucleotide probes (PCR-SSOP). In this study, we found DPA1*01 and DPB1*0202 allele frequencies in HLA class II genes are significantly higher in HNL patients than in normal controls. It is known that the frequency of DPB1*0202 alleles is extremely low or absent in Caucasians (e.g., French 0.4%, Italian 0.8%) and Negroid (e.g., South African 0%, Hottentot 0%), but relatively frequent in Asians (e.g., Korean 9.9%, Japanese 4.5%). Previous reports have said the incidence of HNL is frequent in Asians but rare in other races. In light of this background, HLA class II genes of HNL and the incidence of HNL in Asian countries, including Japan, might have a positive relationship to DPA1*01 and DPB1*0202 allele.

The cervical lymph nodes of 27 patients with histiocytic necrotizing lymphadenitis (HNL) were examined, as were those of 9 patients with tuberculous lymphadenitis (Tb), 10 with reactive paracortical hyperplasia (RPH), and 10 with nonspecific lymphadenitis (NSL). Southern blot analysis, the polymerase chain reaction (PCR), and in situ hybridization were use to locate the human herpesvirus-6 (HHV-6) genome. Southern blot analysis showed that all cases were negative for HHV-6 genomes, although all but one HNL case expressed HHV-6 genome using PCR. On in situ hybridization all 10 HNL cases, 6 of the 10 RPH cases, 6 of the 10 NSL cases, and 2 of the 9 Tb cases showed HHV-6 DNA. These results indicate that the presence of HHV-6 genome is not specifically related to HNL, and that this virus could hibernate in a latent form in the cervical lymph nodes. In addition, we examined three different primers (A, B, and C) for PCR amplification of HHV-6 genomes.

We report a case of histiocytic necrotizing lymphadenitis (HNL) with bone marrow extension in a 29-year-old male in which many large mononuclear cells infiltrated the bone marrow and mimicked malignant lymphoma. A lymph node biopsy confirmed the diagnosis of HNL. Immunohistologically, the infiltrating cells in the bone marrow were positive for lysozyme, LeuM1, Kp-1 and T-cell markers. The cells did not show haemophagocytosis. A skin biopsy from an accompanying facial skin rash revealed a proliferation of large cells similar to those observed in affected foci of the lymph node in subcutaneous tissue. The infiltrating cells were mainly lysozyme and Kp-1-positive histiocytes, some with phagocytosis of nuclear debris but none characteristic of haemophagocytosis. Transformed T-cells were also infiltrating.

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