Immune response to HIV infection

. Immune response to HIV infection
Once the HIV virus replicated, the level of virus increases in the body. This increase induces then a response of the immune system. This response involves the humoral as well as the cell-mediated immunity. This response can be divided in several steps.

1. The free viral particles released into the body are ingested and digested by the macrophages. The small peptides resulting of this digestion are then expressed at the surface of the plasma membrane and act as antigens. Remember that beside its phagocyte function, the macrophage is also able to present antigens to the immune system. It belongs to the APCs class of cells (Antigens Presenting cells). This recognition involves the MHC molecule at the surface of the macrophage and the TcR (T cell Receptor) at the surface of the T Helpers cells.
2. Once the T Helper cell is activated by the binding of MHC/Antigen and TcR/CD4, it secretes cytokines or interleukines which are going to activate other immune cells.
3. One type of actived cells are the lymphocytes B. You have already seen that activation of lymphocytes B results in the production of antibodies specific to the antigen, the HIV viral peptides. At this point we can detect free circulating antibodies in blood. This is the common way to detect HIV infection. For example, before doing any blood transfusion to a patient, doctors use only HIV negative blood. Mention PcR, in this case this technique allows to detect the genetic material of HIV virus when the virus circulates freely into the blood. Even if PcR detection is a more precise way of detection of any virus because we can detect it earlier, it is not the routine test. Then the free antibodies released into the body are going to bind the free virus. The binding occurs because of the specificity. The last step of the humoral response consists in the binding of the complex antibodies/antigens to macrophages via receptor for the constant regions of the immunoglobulins. This binding results in the phagocyte and digestion of the virus and finally in the death of the virus. This is how the humoral immunity depletes our body from HIV viruses.
4. The other response to HIV infection is the cell-mediated response. The secretion by the T Helpers of cytokines and interleukines is also able to activate the lymphocytes cytototix. The activated cytotoxic cells are then able to recognize the infected T Helpers cells. The binding between the NK cells and the infected T Helpers cells results in the death of the infected cells via secretion of lethal molecules.