A highly reliable, sensitive, flow cytometric/fluorometric assay for the evaluation of the anti-HIV activity of antiviral compounds in MT-4 cells

Infection of human T4 lymphocyte MT-4 cells with human immunodeficiency virus (HIV) results in cell death 4-5 days after infection. We have now developed a highly sensitive and rapid procedure for estimating the cytopathic effect of HIV in MT-4 cells. This method is based on fluorometric as well as flow cytometric evaluation of HIV-infected MT-4 cultures. By the use of fluorescein diacetate (FDA), a non-fluorescent diacetyl fluorescein ester that becomes fluorescent upon hydrolysis by esterases present in the cytoplasm of viable cells, as few as 100-200 viable MT-4 cells can be accurately determined. Applying this new method to HIV-infected MT-4 cell cultures treated with differing concentrations of the potent anti-HIV agent azidothymidine (AZT), we obtained a virus-inhibitory dose-response comparable to those obtained by the conventional (labour-intensive and time-consuming) methods. The FDA-based cell viability assay appears particularly suited for the rapid, reliable and sensitive evaluation of potential anti-AIDS agents in cell culture.

Interaction of HIV infection with nervous tissue may play a crucial role in the development of AIDS

In this note, we first review some of the immunopathogenic mechanisms of HIV infection and discuss the possible role of the idiotypic network in producing immunodeficiency; we then propose that the interaction of HIV with the nervous system is such as to generate signals which are misinterpreted by the nervous system: the feedback reaction of the nervous system may play a crucial role in the development of AIDS. We conclude by studying a very simple model for the dynamics of AIDS.

[AIDS and human lymphocytes]

HIV infection is no doubt the primary cause of AIDS. But the relationship between HIV and its host lymphocytes is fairly complicated. It has become clear that the host range of the viruses varies according to the clinical stage of the patients from whom viruses were isolated. Besides, the cause or mechanism of cell killing by HIV infection is not well-known. The density of CD4 molecules on the cell surface can not simply explain the phenomena, such as the level of virus growth, killing mechanisms of lymphocytes and host range of the virus. It is quite interesting to analyse which gene of the virus determines the characteristics of the virus.

Infection of B lymphocytes by the human immunodeficiency virus and their susceptibility to cytotoxic cells

The T4 molecule (CD4) is an important component of the human immunodeficiency virus (HIV) receptor. As yet, no other component has been demonstrated. We report here that two cell lines, a B lymphoblastoid cell line (Gupta) and a glial cell line (HEB) derived from human embryonal brain tissue, are productively infectable with two distinct isolates of HIV as judged by electron microscopy and immunological and virological studies. These two cell lines do not display detectable surface CD4 glycoprotein. However, using S1 nuclease analysis, we have found that both cell lines do express low levels of CD4 mRNA. Neither of them produced syncytia formation upon HIV infection, a recognized feature of HIV-infected cells strongly expressing the CD4 glycoprotein. It is conceivable that the CD4 mRNA is translated, resulting in meager surface expression of CD4 molecules undetectable by conventional techniques. Therefore, infection with HIV may be one of the most sensitive methods of demonstrating low levels of CD4 expression by human cells. Furthermore, HIV-infected Gupta cells have here been shown to be more susceptible to the lytic activity of natural killer (NK) cells than their uninfected counterparts. These phenomena may be important for pathogenesis of HIV-associated disorders.

Entry of human immunodeficiency virus (HIV) into MT-2, human T cell leukemia virus carrier cell line

The ultrastructural features of early events in human immunodeficiency virus (HIV) infection of HTLV-I-carrying MT-2 lymphocytes were investigated by electron microscopy. Within 10 min after virus inoculation at 37 degrees C, the virus entered the cell in two ways; (1) the virus attached to the lymphocyte membrane and the viral core entered the cell after fusion of the viral envelope with the cell membrane, and (2) part of the cell membrane to which the virus was attached became invaginated, the virus became trapped in a phagosome and the viral core entered after the fusion of viral membrane with the vacuolar membrane. Thereafter, some cells were observed to form syncytia with multiple nuclei. When the proportion of anti-HIV antibody-reactive cells present exceeded 90%, virus production was strongly activated, and budding on the cell membrane was frequently observed.