Ahmed Bouzidi

Antibody-Dependent Enhancement of Coxsackievirus B4 Infectivity of Human Peripheral Blood Mononuclear Cells Results in Increased Interferon-α Synthesis

IgG devoid of neutralizing activity and isolated from donor plasma by chromatography formed immune complexes with coxsackievirus B4 (CVB4) and significantly increased the infection of peripheral blood mononuclear cells with CVB4. The major host cells for CVB4 infection enhanced with IgG are monocytic CD14+ cells. The roles of CVB and adenovirus receptor and Fcgamma receptor II and III have been shown. Increased viral replication and the release of infectious particles were demonstrated when interferon (IFN)-alpha produced by infected cells was first neutralized by use of antibodies. The CVB4 IgG-induced synthesis of IFN-alpha by monocytes reflected entry and uncoating of CVB4 but not of viral replication and required the presence of CVB4 RNA inside the cells. Thus, CVB4 can infect monocytes by an antibody-dependent mechanism through interactions between the virus, antiviral antibodies, and specific receptors that result in IFN-alpha production.

Tumor Necrosis Factor Alpha Levels in Plasma and Whole-Blood Culture in Dengue-Infected Patients: Relationship Between Virus Detection and Pre-existing Specific Antibodies

The pathogenesis of dengue hemorrhagic fever (DHF) is not well known, but the role of host factors has been suggested. The level of immunoreactive circulating and cell‐generated tumor necrosis factor alpha (TNFα) was studied in 35 patients with DHF; its relationship with virus isolation and/or genome detection by reverse transcription polymerase chain reaction (RT‐PCR) and specific antibodies were detected by hemagglutination inhibition (HI). Large variation of TNFα plasma levels was obtained in dengue‐infected patients at the same stage of the disease and at the same day after infection. Most of the patients (14 out of 17 patients) who displayed augmented spontaneous in vitro production of TNFα by heparinized whole‐blood culture compared with controls also had elevated levels of TNFα in the plasma. The TNFα values in lipopolysaccharide and phytohemagglutinin heparinized whole‐blood cultures were not higher in patients than in controls, but low TNFα levels were obtained in three out of 30 patients. An inverse correlation was observed between spontaneous in vitro TNFα production and viral replication, which raises the issue of the antiviral effect of TNFα in dengue infection. The results do not support the hypothesis of the role of antibody‐dependent enhancement giving rise to increased viremic titers and production of TNFα in patients. The present study demonstrates the activation of the TNFα‐producing cells in dengue‐infected patients and suggests further investigation to define the mechanism and the role of TNFα in the pathogenesis of dengue virus infection. J. Med. Virol. 54:210–218, 1998.

Human antibodies isolated from plasma by affinity chromatography increase the coxsackievirus B4-induced synthesis of interferon-alpha by human peripheral blood mononuclear cells in vitro.

Coxsackievirus B4 (CVB4) can be found in circulating blood of patients; however, the interaction of CVB4 with peripheral blood mononuclear cells (PBMCs) is poorly understood. CVB4 induced low levels of IFN-alpha synthesis in PBMCs from healthy donors. In contrast, preincubation of infectious CVB4 with plasma from these donors containing anti-CVB4 antibodies strongly enhanced the synthesis of IFN-alpha. IgG obtained from plasma by chromatography formed immune complexes with CVB4 and increased significantly the CVB4-induced production of IFN-alpha by PBMCs. These antibodies did not have a neutralizing effect on CVB4 infection of Hep-2 cells. The role of CVB and adenovirus receptor (CAR), FcgammaRII and FcgammaRIII in the increased synthesis of IFN-alpha induced by CVB4 preincubated with IgG was shown by inhibition with specific antibodies. The major interferon-alpha-producing cells in response to CVB4-IgG complexes were CD14(+) cells and monocyte-enriched PBMCs. With the latter, detection of IFN-alpha by immunostaining was positive whereas in monocyte-depleted PBMCs it was not. This study shows that CVB4-induced synthesis of IFN-alpha by PBMCs can be enhanced by an antibody-dependent mechanism through interactions between the virus, non-neutralizing antivirus antibodies, FcgammaRII and III and CAR.

Role of Interferon Alpha (IFN-α) and Interferon Gamma (IFN-γ) in the Control of the Infection of Monocyte-Like Cells with Human Cytomegalovirus (HCMV)

The role of cytokines in the control of HCMV infection has been studied in THP‐1 cells, a macrophage‐like cell model and in MRC‐5 cells. HCMV replication was studied by immune detection of viral immediate‐early antigens (IEA) and virus yield was evaluated in MRC‐5 cells by immunoperoxidase staining. Pretreatment of MRC‐5 and phorbol 12‐myristate 13‐acetate (PMA)‐treated THP‐1 cells with IFN‐α or IFN‐γ for 24 hr prior to the infection reduced the number of infected cells and virus yield. A synergistic anti‐CMV activity in synthesis of early proteins was obtained with these cytokines in combination with TNF‐α in differentiated THP‐1 cells only. Treatment of HCMV‐infected differentiated THP‐1 cells or MRC‐5 cells with IFN‐α or IFN‐γ alone had no inhibitory effect on virus replication, however the virus yield was reduced with ganciclovir. A synergistic anti‐CMV activity in virus yield was obtained only when infected differentiated THP‐1 cells were treated with ganciclovir in combination with IFN‐γ. The current study shows that IFN‐α and IFN‐γ can play a role in the reduction of HCMV replication in macrophage‐like cells and in the efficiency of therapies with ganciclovir in this cell type and that the anti‐CMV effect of cytokines may be different in fibroblasts and in macrophage‐like cells.