Table 1.
Comparison of HIV-1 and HIV-2 infection.
| Human immunodeficiency virus (HIV)-1 | HIV-2 | |
|---|---|---|
| Epidemiological and clinical significance between HIV-1 and HIV-2 infection | ||
| Geographical distribution | Global | Confined to West Africa with limited spread; also reported in former Portuguese colonies, such as Angola, Mozambique, and Brazil, and in parts of India |
| Heterosexual transmission | Sexual mode of transmission is higher | Fivefold lower rate than HIV-1 |
| Vertical transmission | Mother to child transmission is higher | 20- to 30-fold lower rate than HIV-1 |
| Duration of asymptomatic stage | Time to develop acquired immune deficiency syndrome (AIDS) varies, ranging from a few months to many years, with an estimated median time of 9.8 years | Longer duration, ranging from 10–25 years |
| Clinical illness | If untreated, around half of people infected with HIV-1 will develop AIDS within 10 years | 86–95% of people infected with HIV-2 are long-term non-progressors |
| Proviral DNA load | Similar | Similar |
| Plasma RNA load | Higher | Significantly lower than HIV-1 |
| Viral replication kinetics | Higher replication and 100-fold more fit | Transient replication and less fit |
| Infectivity and transmission fitness | Similar and 100-fold more fit | Similar and less fit |
| Co-receptor usage | Uses CXCR4 and CCR5 | Uses a range of co-receptors, including CCR1, CCR2, CCR3, CXCR6, BOB, CCR5, and CXCR4 |
| CD4+ T-cell responses between HIV-1 and HIV-2 infection | ||
| CD4+ T-cell count | Lower compared to HIV-2 with undetectable viral load but similar to HIV-2 with higher viral load | Higher in HIV-2 with undetectable viral load and similar to HIV-1 with higher viral load |
| CD4+ T-cell response | Lesser proliferative capacity and polyfunctionality, and increased differentiation | Better proliferative capacity, more polyfunctionality, and lesser differentiation |
| Thymic function | HIV-1 can replicate efficiently in thymus tissue. No correlation with the rate of CD4+ T-cell loss | HIV-2 is able to infect the human thymus, but this is associated with limited viral replication. Correlates with lower rates of CD4+ T-cell |
| Production of cytokines | Interleukin (IL)-2- and IL-4-producing cells decline as disease progresses | IL-2- and IL-4-producing cells better preserved. Expressions of both IL-2- and IFN-γ-producing cells are more |
| CD57−CD4+ T-cell expression | Less frequently seen | More CD57− cells are seen |
| CD4+ T-cell activation level | Positive correlation between lipopolysaccharide (LPS) level and proinflammatory cytokines IL-12 and IFN-γ | Negative correlation between LPS level and proinflammatory cytokines in HIV-2 individuals with undetectable VL |
| Susceptibility to the SAMHD1 | Myeloid cells are refractory to viral infection | Presence of Vpx permits viral infection of myeloid cells through degradation of SAMHD1 |
| Immune activation and T-cell apoptosis | Higher immune activation and more apoptosis | Less immune activation and less T-cell apoptosis |
| Nef | Does not downmodulate the TCR–CD3 complex | Downregulates the TCR–CD3 complex |