Interleukin-4 is needed for the infection of monocytes by human cytomegalovirus.

OBJECTIVE: We studied the ability of human cytomegalovirus (HCMV) to infect peripheral blood mononuclear cells (PBMC) pretreated with or without Th2-cytokine interleukin-4 (IL-4) in vitro. METHODS: Adherent cells and nonadherent cells were obtained from PBMC. We inoculated these cells with HCMV at concentrations ranging from 0 to 10 ng/ml of IL-4. Immediate-early antigen-1 (IE-1) and glycoprotein H (gH) mRNAs were detected using the reverse-transcription polymerase chain reaction. RESULTS: IE-1 and gH mRNAs could be detected in monocytes pretreated with IL-4. In contrast, no IE-1 mRNA was detected in monocytes pretreated without IL-4. We tested whether higher infectious titers could result in the infection of monocytes whether or not they were pretreated with IL-4. However, no IE-1 mRNA was detected in the monocytes not pretreated with IL-4. To elucidate how HCMV-infected monocytes affect lung tissue, human embryonic lung fibroblasts MRC-5 were cocultured with HCMV-infected monocytes. The cytopathic effects of HCMV were observed microscopically and was confirmed by direct immunoperoxidase staining with a human monoclonal antibody against the HCMV IE-1. CONCLUSION: Our data strongly suggest that the ability of HCMV to infect monocytes may correlate with the presence of IL-4.

In vitro transmission of HCMV between fibroblasts and peripheral blood leukocytes in the presence of IL-4.

We demonstrated transmission of human cytomegalovirus (HCMV) from the human lung fibroblast MRC-5 to peripheral blood leukocytes (PBLs). mRNA of the HCMV immediately-early (IE) antigen was detected in PBLs cultured with IL-2 or IL-2 + IL-4 that made direct contact with HCMV-infected MRC-5, whereas it was not detected in PBLs prevented from making cell-to-cell contact. However, mRNA of HCMV IE was not detected in PBLs cultured with IL-2 and IFN-gamma that made direct contact with HCMV-infected MRC-5. Transmission of the pp65 antigen was increased in culture medium containing IL-4. At a higher viral infection titer, cell-free HCMV infected adherent PBLs cells. The subset, which did not adhere, did not infect cell-free viruses even at a very high multiplicity of infection. Moreover, the adhered subset of PBLs infected with HCMV was able to transmit HCMV to non-infected fibroblasts. Our results suggest that cell-to-cell contact (when PBLs make direct contact with HCMV-infected cells) is important in the mechanism of HCMV transmission and that the adherent cells of PBLs are one of the most important vehicles for HCMV infection. Moreover, we suggest that type 2 cytokines such as IL-4 enhance the transmission of HCMV to PBLs.

Identification of the HLA-A24 peptide epitope within cytomegalovirus protein pp65 recognized by CMV-specific cytotoxic T lymphocytes.

Among cytomegalovirus (CMV) tegument proteins, phosphoprotein 65 (pp65) has been identified as the important target antigen of the cytotoxic T lymphocyte (CTL) response against the virus. We synthesized seven CMV-pp65-derived peptides carrying an HLA-A24-binding motif, and investigated the ability of these peptides to induce CMV-specific CTL. We identified one nonamer peptide (pp65113-121; VYALPLKML) able to bind HLA-A24 and induce CTL responses in vitro in peripheral blood mononuclear cells (PBMC) from CMV-seropositive individuals. The peptide-specific CTLs generated were capable of recognizing pp65 expressed on CMV-infected fibroblasts as well as pp65113-121 peptide bound to the surface of C1R-A*2402 cells in an HLA-A24-restricted manner. The pp65113-121 peptide thus might be considered a synthetic peptide vaccine in HLA-A24-positive individuals.