Antibody mediated enhancement of HIV-1 infection of an EBV transformed B cell line is CD4 dependent

Antibody-dependent enhancement of viral infection: molecular mechanisms and in vivo implications

Besides the common receptor/coreceptor-dependent mechanism of cellular attachment, some viruses rely on antiviral antibodies for their efficient entry into target cells. This mechanism, known as antibody-dependent enhancement (ADE) of viral infection, depends on the cross-linking of complexes of virus-antibody or virus-activated complement components through interaction with cellular molecules such as Fc receptors or complement receptors, leading to enhanced infection of susceptible cells. Recent studies have suggested that additional mechanisms underlie ADE: involvement of complement component C1q and its receptor (Ebola virus), antibody-mediated modulation of the interaction between viral protein and its coreceptor (human immunodeficiency virus) and suppression of cellular antiviral genes by the replication of viruses entering cells via ADE (Ross River virus). Since ADE is exploited by a variety of viruses and has been associated with disease exacerbation, it may have broad relevance to the pathogenesis of viral infection and antiviral strategies.

Expression of the mouse Fc receptor B2 in bovine cells rescues the infectivity of conditionally neutralized bovine viral diarrhea virus

We examined the infectivity of bovine viral diarrhea virus (BVDV) particles opsonized with monoclonal antibodies on bovine cells expressing the murine Fcgamma receptor B2 (FcgammaRB2). Incubation of BVDV with each of five monoclonal antibodies (Mabs) to the envelope glycoprotein E2 led to efficient virus-neutralization, as evidenced by the failure to infect standard bovine testicle cells. In contrast, inoculation of four of these Mab-virus complexes onto transfectant bovine testicle cells expressing FcgammaRB2 resulted in a significant rescue of virus infectivity. Mab-virus complexes were 13.1, 7.37, 5.56 and 4.49 times more infectious for FcgammaR-expressing cells than for cells lacking FcgammaR. Because Mab-opsonized BVDV virion complexes uninfectious for standard cells may initiate productive infection in cells expressing the FcgammaR, the virion-Mab interaction should be described as a conditional neutralization. Interestingly, the infectivity of BVDV complexed with a specific virus neutralizing Mab (10f9) could not be rescued in FcgammaRB2-expressing cells. We postulate that attachment of antibody-virus complexes to FcR may only result in productive infection if the binding of antibody to virions does not interfere with post-attachment entry functions. Conditionally neutralized virions may play a role in the pathogenesis of any of the multiple diseases resulting from BVDV infections in cattle.

Non-radioactive PCR method for quantification of HIV-infected peripheral blood mononuclear cells in HIV-positive subjects

A nested PCR method for quantification of HIV-infected peripheral blood mononuclear cells (PBMC) which does not use radioactivity nor plasmids is described. Quantification was achieved by means of limiting dilutions and an ACH2 cell standard. The method was used to study 23 HIV-infected patients. A significant correlation was seen between the stage of HIV disease, as classified by CDC criteria, and the number of infected PBMC. Although the CD4+ cell count also correlated well with the stage of HIV disease, there was only weak correlation between the result obtained by the PCR method and the CD4+ cell count.

Infection of epithelial cell line HEp-2 with human immunodeficiency virus type 1 is CD4 dependent

HEp-2 cells, human epithelial cells derived from a larynx carcinoma, were found to be highly susceptible to infection with HIV-1 stain IIIb and MN, but not to infection with the monotropic strain IIIBa-L or the clinical isolate HIV-1AT. HEp-2 cells infected with HIV-1 IIIb continuously secreted high levels of p24 antigen, while no cytopathic effects were observed. Although no CD4 antigen could be detected on the cells by flow cytometric analysis, CD4 mRNA was detected by reverse transcriptase PCR. Furthermore, infection could be blocked by anti-CD4 monoclonal antibody OKT4a indicating a CD4 mediated viral entry in HEp-2 cells. HEp-2 cells are commonly used in clinical virology for the culture of different viruses from clinical specimens. HEp-2 cells should therefore be handled with caution as they may potentially become infected with HIV.