In this article we will discuss about the working of immune system in the presence of HIV.
Infection is carried out through the spicules present on envelope of HIV which attach to the target cell. The gpl20 has affinity for a specific molecule, the T4 or CD4 molecule exposed on the surface of certain cells i.e. lymphocytes.
The lymphocytes secrete T4 molecules and play a major role in the immune system, and AIDS symptoms are expressed after their destruction. Function of immune system is a complicated process (Fig. 17.47).
The infected host cells rapidly produce antibodies against gp120 which is recognised as a foreign molecule or an antigen. Some of the antibodies attach to the envelope and block the connection of virus to T4 molecules of the target cell.
Even the large quantity of neutralizer antibodies is not capable of stopping the dissemination of HIV. Thus the infected individual causes infection to his/her sexual partner of those receiving blood. The provirus may remain silent for a long period without showing any sign of presence.
In response to introduction of an infected cell into the organism the macrophages are the first to intervene. They have the capacity to catch the viral particles, then cut them into pieces and prevent as antigen to the T4 lymphocytes. The T4 lymphocytes become incapable to secrete interleukins, a soluble substance which can communicate to other cells of immune system for the presence of antigens.
The T4 lymphocyte is known to induce the proliferation and maturation of B-lymphocytes which then produce antigen specific antibodies. As the disease evolves, it loses the capacity to produce antibodies. The infected macrophages serve as the reservoir of viruses and disseminate HIV to all the tissues. They become weakened and their function becomes diminished.
The action of T4 lymphocytes takes place on another category of lymphocytes (T8 lymphocyte) which can either kill the infected cell (T8 cytotoxic effect) or inhibit the immune response (T8 suppressors). The T4 markers are not present on T8 lymphocytes.
They are capable of killing the cells through direct contact and, therefore, they are called cytotoxic lymphocytes. T lymphocytes have the long life of several months to years and represent to about 60-80% of total lymphocyte population. T8 lymphocytes are resistant to HIV.
It carries on its surface a protein of an antigen against which the T8 lymphocyte has been sensitized. It also carries on its membrane surface the antigens of histocompatibility of self markers called the HLA antigen (human lymphocyte system A). But their role of antiviral protectors turns them into formidable demolition agents.
Through the elimination of infected cells, they clean up the organisms or its infected centres, while doing this they eliminate the cells which carry out immune functions. This is how T4 lymphocytes, B- lymphocytes and infected macrophages can be rapidly destroyed when they are recognised as the targets by the cytotoxic lymphocytes.
Inflammatory reactions are brought about by the release of toxic products which attack the surrounding tissues such as pulmonary inflammation of immune origin among the HIV carriers.
Unfortunately, in case of AIDS, T4 cells are first attacked which are destroyed later on. The other cells such as B-lymphocytes and macrophages are also destroyed. Thus, in overall struggle the immune system is destroyed and HIV gets upper hand.