Interferon and Natural Killer Activity in Infants with Exanthem Subitum
Blood from patients diagnosed as suffering from exanthem subitum (roseola infantum), a common disease of infancy, was studied during the febrile, rash (exanthem), and convalescent phases. Investigations were undertaken to determine how infants are able to begin fighting the disease despite an average time lag of five to seven days before significant levels of HHV -6 specific antibody titer is seen. Natural killer (NK) cytotoxicity assays were conducted using 51 Chromium labelled K562 targets. Patient antibody titer against HHV -6 was measured through the use of a monoclonal antibody immunofluoresence test. Interferon (IFN) levels were analyzed in vivo, and the ability of the three classes of interferon to induce resistance to HHV -6 in cord blood mononuclear cells was studied In vitro. In comparison to a healthy adult control, infants with exanthem subitum in the acute phases of the disease displayed significantly elevated levels of NK activity. By the time convalesence had begun, NK cytotoxicity had fallen to levels below that of the same control. Interferon showed a similar pattern, with leukocyte interferon (IFN-a) seen to be the primary component. In vitro work indicated some resistance conferred by both IFN -a and. IFN -b; other studies with the different members of the human herpesvirus family have also shown that IFN-a can play a role in antiviral resistance. These results suggest that natural killing and interferon stimulation of NK and/or target cells play a key role in the ability of infants to combat HHV -6 infection, and that further studies for treatment of immunosuppressed or immunodeficient adults suffering from HHV-6 infection may proceed along these lines .
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