A combination of immunological reaction to a drug and HHV-6 reactivation results in the severe course of DIHS. The demonstration of HHV-6 reactivation is a useful marker of diagnosis as well as prognosis in DIHS.

Background: A severe adverse reaction to sulfasalazine therapy has been associated with hypersensitivity syndrome, the clinical features of which are similar to infectious mononucleosis. No serologic evidence of viral infections has been reported with this syndrome; however, human herpesvirus 6 infection has not been specifically investigated, which could cause an infectious mononucleosislike syndrome.Observations: We report 2 cases of hypersensitivity syndrome induced by the use of sulfasalazine. The clinical features of the syndrome appeared 18 and 32 days after administration of sulfasalazine. Clinical signs included a maculopapular rash progressing to exfoliative eryth-roderma, fever, and lymphadenopathy. Leukocytosis, atypical lymphocytes, liver dysfunction, and renal disturbance were also observed. In 1 patient, human herpesvirus 6 variant B was isolated from peripheral blood mononuclear cells, and in both patients anti-human herpesvirus 6 IgG titers increased considerably.Conclusions: Two cases of hypersensitivity syndrome due to sulfasalazine use were associated with the reactivation of human herpesvirus 6, which may be a required cause of hypersensitivity syndrome.

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Approximately one kilobase pairs surrounding and upstream the transcription initiation site of a cloned ribosomal DNA (rDNA) of the mouse were sequenced. The putative transcription initiation site was determined by two independent methods: one nuclease S1 protection and the other reverse transcriptase elongation mapping using isolated 45S ribosomal RNA precursor (45S RNA) and appropriate restriction fragments of rDNA. Both methods gave an identical result; 45S RNA had a structure starting from ACTCTTAG---. Characteristically, mouse rDNA had many T clusters (greater than or equal to 5) upstream the initiation site, the longest being 21 consecutive T's. A pentadecanucleotide, TGCCTCCCGAGTGCA, appeared twice within 260 nucleotides upstream the putative initiation site. No such characteristic sequences were found downstream this site. Little similarity was found in the upstream of the transcription initiation site between the mouse, Xenopus laevis and Saccharomyces cerevisiae rDNA.

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