We report 2 cases of nonspecific postvaccinial dermatitis following smallpox vaccination. The patients presented with diffuse, pruritic, erythematous macules and papules 11 days (case 1) and 7 days (case 2) following routine smallpox vaccination. Biopsies of the lesions demonstrated spongiotic dermatitis without evidence of viral cytopathic changes. One case showed a pityriasis rosea-like histologic pattern. The exanthema resolved without sequelae with symptomatic treatment (case 1). Review of historical literature demonstrated the association of a variety of nonspecific cutaneous complications with vaccinia inoculation, including erythema multiforme, urticaria, and pityriasis rosea. The association of these various dermatitides with smallpox immunization is not well known and is likely underreported.
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The purpose of vaccination against viruses is to induce strong neutralizing antibody responses that inactivate viruses on contact and strong T cell responses that attack and kill virus-infected cells. Some viruses, however, like HIV and hepatitis C virus, are only weakly controlled by neutralizing antibody, so T cell immunity is very important for control of these infections. T cells recognize small virus-encoded peptides, called epitopes, presented on the surface of infected cells, and some of these epitopes induce strongly protective and others weakly protective T cell responses. However, the same T cells can sometimes demonstrate cross-reactivity and recognize similar epitopes encoded by two different viruses. We questioned here what infection with a virus encoding a weak cross-reactive epitope would do to immunity to a previously-encountered virus. Here we report that such an infection can compromise protective immunity by enhancing the normally weak response and suppressing the normally strong response. Under these conditions such epitopes function as “pathogenic” epitopes, and we suggest that the potential for inducing responses to pathogenic epitopes should be an important consideration in the design of T cell vaccines.
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