The decline in CD4+ T lymphocytes as a function of the duration of HIV infection, age at seroconversion, and viral load.

BACKGROUND: The rate of CD4+ T-lymphocyte decline seen in HIV-infected patients is very variable. Although older patients, a longer duration of HIV infection, and a high level of plasma viraemia, have been associated with a faster fall in CD4+ T-cells, the relationship between these variables is still not well known. PATIENTS AND METHODS: In a cross-sectional study that included a total of 107 patients of known age and date at HIV seroconversion, the current CD4+ T-cell count and plasma viraemia were examined. Patients were not taking antiretroviral drugs, nor had received immunizations nor were suffering any intercurrent infections at the time of the study. RESULTS: The mean duration of HIV infection was 8.6+/-2.9 years. The mean CD4+ T-lymphocyte count was 367+/-264 x 10(6)/l. Mean plasma viraemia was 4.3+/-0.9 logs. In a linear regression model, the current CD4+ T-cell count was explained in 21.7% by the duration of HIV infection, while the level of plasma viraemia justified separately up to 37.0%. When both parameters were combined, they explained 58.8%. of the CD4+ lymphocyte values. In this model, a variation of one logarithm in the plasma viraemia had six times greater effect on the number of CD4+ lymphocytes than each year of HIV infection. When the age at seroconversion was added to the model, the CD4+ cell count allowed the explanation of up to 62.2% of cases. CONCLUSIONS: The age at seroconversion, the duration of HIV infection, and the level of plasma viraemia independently and substantially influence the current CD4+ lymphocyte count in HIV-infected subjects. However, other variables should exist (e.g. virus syncytium-inducing phenotype, host immunogenetic repertoire, etc.), contributing to explaining the different rate of CD4+ T-cell decline seen in HIV-infected subjects.