The Effects of HIV Infection on the Immune Response:
Infection with the human immunodeficiency virus (HIV) represents something of an immunological paradox, in tgat HIV induces a strong antiviral immune response, whilst simultaneously and progressively disrupting the ability of the immune system to respond to new infections and antigens, ultimately leading to a severe immune deficiency of the cell mediated immune system:
Infection with HIV is associated in the majority of cases with the production of virus specific antibody.
Some of which can be shown to beutralise the virus in vitro.
In addition, there is a strong virus specific CTL response to the virus in the majority of patients (which is associated with an initial and dramatic fall in virus titre).
This CTL response does not appear able to clear the virus, however, and persistent infection follows.
There is a progressive decline in the number of CD4 + T cells over time, which often accelerates as the patient progresses towards AIDS, at which the CTL response falls away and viral titres rise.
HIV uses the CD4 surface marker sd its receptor for gaining entry to cells. HIV therefore predominantly infects CD4 + cells, and leads to a disruption of the function of these cells , and a progressive decline in their numbers. As described previously, CD4 + T cells play a central role in regulating the immune response, and so HIV infection leads to a disregulation of many aspects of the immune response, including defective antibody and T cell responses to new antigens, and decreased NK responses.
These effects can be detected even when numbers of CD4 + T cells are relatively normal > As CD4 T cell numbers decline, however, the defects become more marked, leading to a state of immunodeficiency which leaves the host susceptible to infection with a variety of common or opportunistic infections and to certain types of tumours .