Absence of Epstein-Barr virus-specific, HLA class II-restricted CD4+ cytotoxic T lymphocytes in infectious mononucleosis.
Cytotoxic T lymphocytes (CTL) with the CD4+ phenotype that recognize major histocompatibility complex (MHC) class II antigens are detectable very frequently in cultures of human alloreactive or virus-specific T cells. The significance of these CD4+ CTL for an immune reaction in vivo is not clear. Since Epstein-Barr virus (EBV) transformed B cells express HLA-class I and class II antigens equally well both CD8+ and CD4+ CTL should be stimulated during an acute EBV infection. We analysed the MHC specificity and the phenotype of EBV-specific CTL from patients with infectious mononucleosis (IM). When tested directly without any previous culture, T cells from patients in the acute phase of IM showed specific MHC-restricted cytotoxicity against the autologous B cell line. Addition of a HLA class I specific monoclonal antibody (MoAb) but not of a HLA class II specific MoAb resulted in a complete blocking of the lytic activity. Cell sorting revealed that the entire cytotoxic activity was present in the CD8+ fraction whereas no specific CTL were detectable in the CD4+ fraction. The absence of cytotoxicity in CD4+ cells was not due to a lack of activation of these cells since both CD8+ and CD4+ cells were activated in situ, showing spontaneous growth in interleukin-2 (IL-2) and expressing the activation marker TP103. Frequency estimation revealed that 1/300-1/600 CD8+ but only 1/2000-1/4000 CD4+ T cells gave rise to a specific CTL colony after 10 days. If CD4+ colonies were tested repeatedly for cytotoxicity we found that CD4+ CTL acquired their cytotoxicity during in vitro culture. In addition, we isolated EBV-specific CD4+ T cell clones able to lyse their stimulator cells in the presence but not in the absence of lectin, even after a long period of culture. Taken together our results show that cytotoxicity mediated by CD4+ T cells does not play a role in an anti-viral immune response.
Department of Medical Microbiology and Immunology, University of Ulm, West Germany.
K H
KH
Enssle
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B
Fleischer
D000956:Antigens, Viral / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D002478:Cells, Cultured; D000939:Epitopes / Q000276:immunology; D006680:HLA Antigens / Q000276:immunology*; D004854:Herpesvirus 4, Human / Q000276:immunology*; D006801:Humans; D007244:Infectious Mononucleosis / Q000276:immunology*; D008213:Lymphocyte Activation; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
D000956:Antigens, Viral; D000939:Epitopes; D006680:HLA Antigens