The Role of Follicular Dendritic Cells in Human Immunodeficiency Virus Pathogenesis

• Main Author: Heath, Sonya Lynn
• Format: Others
• Published: VCU Scholars Compass 1995
• Subjects: Microbiology
• Online Access: http://scholarscompass.vcu.edu/etd/4912; http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=5997&context=etd

Infection with Human Immunodeficiency Virus-1(HIV) results in a disease process characterized by three stages: an acute phase characterized by viremia, a clinically latent stage with little or no detection of virus in the blood, and the last stage, AIDS, which. is characterized. by marked immunodeficiency. During clinical latency, CD4+ T cells decline over a period lasting from a few to several years. Throughout this period, HIV is found trapped on the surface of follicular dendritic cells(FDC) in the germinal centers of secondary lymphoid tissues and this is the primary site of active viral replication. We hypothesize that FDC, and the unique microenvironment they help provide, play a critical role in HIV pathogenesis. The objective of these studies was to begin to characterize the role of FDC in HIV pathogenesis by determining if HIV immune complexes trapped on FDC are infectious. To begin to test this, HIV(IIIB) immune complexes were formed by incubating' virus with serum from. HIV infected individuals as a source of virus-specific antibody. Highly enriched tonsilar FDC (from non-infected individuals)were then incubated with these HIV-complexes to allow FDC trapping in Vitro. HIV binding to FDC was confirmed by electron microscopy(EM). Unbound HIV was removed by washing the cells and FDC bearing HIV immune complexes or control FDC were cultured for four days with superantigen activated, FACS sorted, autologous CD4+ tonsilar T lymphocytes to determine if the T cells could be infected by the FDC trapped virus. HIV infection was detected using PCR amplification of proviral gag sequences that would be present in DNA isolated from the cultures. To ensure that our in Vitro cultures were representative of in vivo events, we used a xenogeneic model where HIV immune complexes were formed and trapped on murine FDC in Vivo. Immune complexes were formed by injection of virus-specific antibody followed by HIV (IIIB). Murine FDC bearing HIV trapped in vivo were isolated and incubated with activated human CD4+ T cells as the only source of virus for infection. Infection was assessed as before. HIV infection of T cells was detected in cultures containing FDC bearing HIV immune complexes trapped in vitro whereas no infection was detected in controls. Furthermore, murine FDC bearing in vivo trapped HIV immune complexes also infected human CD4+ T cells. In some in Vivo experiments, HIV immune complexes were formed using a neutralizing antibody that could block infection. FDC bearing these neutralized HIV immune complexes also transmitted infection to T cells. This prompted the hypothesis that FDC may be able to negate the effects of neutralizing antibody. To test this, we formed HIV immune complexes with several doses (picogram to milligram) of neutralizing antibody and cultured these with T cells ± FDC. No infection was present in cultures of immune complexes and T cells without FDC, however, infection was clearly seen when FDC were added. Furthermore, neither macrophages, dendritic cells, nor FDC depleted populations of tonsilar cells could replace FDC in negating the effect of neutralizing antibody and this effect could be observed with different neutralizing antibodies and several strains of virus including a primary isolate. These data indicate that FDC associated HIV is infectious and that FDC can negate the effects of high levels of neutralizing antibody thus permitting infection to occur. This finding may help explain why HIV infected individuals with neutralizing antibody still have ongoing infection. In addition, this data may cause us to reshape our thinking about vaccination and treatment strategies. Finally, this work supports our hypothesis that FDC play an important role in HIV pathogenesis.