Basic Immunology of the HIV Infection
Transmission and the Initial First Line of Defense
HIV is transfered through direct contact of bodily fluids, through sex, needle sharing, and breast milk. Blood contains the highest concentration fo the virus ahead of semen then vaginal fluid and at the lowest concentration, breast milk. (#3) The skin, vaginal lining, and saliva help provide the first barrier to getting infeted. Skin and membrane layers provide a barrier function and are actually part of the innate system.
HIV and its Destructive Life Cycle
HIV can infect many different cells in the body and even brain cells, but it specifically targets the CD4+ lymphocyte which is a T cell. The virus binds to the CD4+ receptors and co-receptors such as CCR5 or CXCR4 which lie on the surface of the cell. Next the cell uses an enzyme called reverse transcriptase to transcribe and integrate the RNA from the virus into DNA and integrate into the host's genome. When the host cell becomes activated it is then programmed to manufacture the enzymes of the virus as well as other proteins. Protease, another enzyme, cuts the longer HIV proteins into individual proteins and these proteins along with the genetic material of the virus come together to form the virus. the last stage of the HIV life cycle happens when the virus pushes itself out of the host cell and takes away part of the membrane of the cell which allows it to infect other CD4+ cells in the immune system. (#23)
The Innate Immune System Response
The immune system protects the body from invading pathogens and antigens, foreign molecules that stimulate an immune response. Innate defenses act almost immediately within the pathogen's appearance in the body. As HIV enters the system, macrophages, natural killer (NK) cells, and dendritic cells (DC) come to the site of infection immediately.Innate defenses include the skin, cilia in muccus membranes, nasal secretions, saliva and phagocytic cells. Phagocytes migrate to the afffected areas and engulf pathogens. White blood cells, a type of phagocyte, migrate to the areea which causes redness or inflammation associated with infection. Some cells also known as dendritic cells, have a special role in that they regulate the immune response by deviding whether or not the infection requires the use of the adaptive response. (#53)
Innate Response to Adaptive Response
Since the innate system is the body's first response to infections, it may not have all the necessary resources to get rid of an infection. This is where the adaptive immune response comes into play. Whereas innate responses can react immediately, adaptive responses can take up to 7 days to start fighting the virus because it requires the immune system to identify the foreign invaders and learn their behaviors. Dendritic cells help transition the immune system from a state of innate response to an adaptive response. (#54)
The Adaptive Immune System Response
The dendritic cells trigger the adaptive immune response by deciding if the foreign invaders are dangerous. The innate immune cells stimulate a specialized froup of white blood cells known as CD4+ helper T cells. CD4+ refers to a surface protein on the special T cells. These T cells can stimulate an another group of white blood cells called B cells which can produce antibodies that bind to the antigen and immobilize it, thus preventing it from causing infection. CD4+ cells can also send signals to the CD8 killer cell, or cytotoxic cell, which can destroy pathogens. Once activated, memory cells then are produced in order to initiate a stronger cell response if there is re-exposure to the same pathogen. One reason
why HIV is such a hard virus to fight is that it attacts helper T cells. Without enough CD4+, the immune sytem cannot signal B cells to produce antibodies or CD8+ T cells to kill infected cells. Once the virus depletes the helper T cell population the body is no longer able to signal specific immune responses which results in the susceptibility to other infections. As a result, this period is known as the acquired immunodeficiency sydrome or AIDS. (#53)
