HIV is an infection of the lymphoid tissues.

Data show that the replication of virus is rapid in lymphoid tissue (Ho et al, 1996).

Virus seen in the periphery is "spillover" from the lymphoid tissue. Between 10⁹ and 10¹⁰ virions are produced daily and they are cleared from the plasma with a half life of approximately 1.5 days.

Infected cells finally are destroyed by virus or die and are rapidly replaced but finally the destruction results in depletion of lymphoid cells and the development of immunodeficiency.

With the rapid turnover of virus there is attendant frequent viral mutation.

The mutations confer tropism changes that result in escape from neutralising antibody or therapeutic drugs.

As the lymphoid cells are destroyed the virus, escaping the immune system mechanisms, increases, the peripheral CD4⁺ cells are depleted, the peripheral viral load increases and the immune function of the host is depleted.