A unified approach to modeling the HIV infection in pediatric and adult AIDS risk groups

The best surrogate immunological marker of the progression of the HIV infection towards AIDS is shown to be the percentage of lymphocytes that are CD4+ T cells (CD4%); this marker permits a unified description of the infection in all risk groups, pediatric as well as adult. An analysis of the data shows that although a below average CD4% is a necessary condition for the development of AIDS, it is not sufficient; there is no critical CD4 value below which an infected immediately develops one of the opportunistic infections characteristic of clinical AIDS. An analysis of CD4 cell density data suggests that the time-dependence of a cohort's mean CD4 density after infection with HIV is independent of its preinfection value. This result implies that the length of the incubation period for developing AIDS in an infected is independent of the subject's preinfection CD4 density value. An analysis of the HIV incubation period distributions for the various AIDS risk groups indicates that the distributions are represented by mathematically different curves, probably due to differences in viral load at infection time in the adult risk groups. An immunological model is advanced which could correctly explain why viral propagation in the lymphatic organs in homo sapiens continues throughout the incubation period until the organs' viral burden destroys their ability to function properly. This model also describes the possible critical event that triggers the onset of clinical AIDS.