The Role of Viral Load in the Pathogenesis of HIV-2 Infection in West Africa

The role of Human Immunodeficiency Virus type 2 (HTV-2) viral load has been studied in West Africa in order to understand how this infection differs from HIV-1 and why the majority of HIV-2 infected individuals live for long. Using a polymerase chain reaction (PCR) based-assay, it was found that the level of HIV-2 provirus was surprisingly high in HTV-2 seropositive people who live long without sign of immunosuppression; in contrast the rate of HIV-2 replication reflected by RNA viral load was found low. However, HIV-2 replicates to a high titre in some HIV-2-infected people whose disease progresses rapidly to death. Longitudinal follow-up demonstrated that baseline HIV-2 RNA viral load predicts the rate of CD4+ T cell decline and death but the level of proviruses is a less sensitive predictor. Cytotoxic T-lymphocyte activity (CTL) against HIV-2 structural proteins, especially Gag, was found in most HIV-2 infected people and was inversely correlated with HIV-2 proviral load. Strong CTL activity was consistently found in people who did not have progressive disease, suggesting that CTL play an important role in controlling HIV-2 replication. Co-infection with human T-lymphotropic virus type I (HTLV-I) occurred frequently in HIV-2-infected people in a village in Guinea-Bissau but did not seem to enhance HIV-2 viral load. However an increase in HIV-2 viral load was found in an HIV-2-infected individual with malaria parasitaemia, suggesting that malaria infection enhances HIV-2 viral load. The majority of people who are dually seroreactive for both HIV-1 and HIV-2 arc infected with both viruses but some subjects are dually seroreactive because antibodies against one type cross-react with the other type of HIV. These cross-reactive antibodies may be distinguished by antibody dilution analysis. Other dually seroreactive people harbour an undetectable level of HIV-2 provirus and HIV-2 proviral load tended to be low in advanced disease while HIV-1 proviral load was high