Thursday, October 6, 2011

HIV (Human Immunodeficiency Virus)

One of the scariest virus around is the RNA virus called HIV! Once thought to have originated from Africa is now found worldwide.

What are the symptoms you would have to look out for?
Well, the progress of this disease can be categorized into 4 stages:
  1. First Phase: Most individuals will have no symptoms, but some might develop a rash, flu, and swollen lymph glands.
  2. Second Phase: Production of anti-HIV rises in blood stream. Although the level of HIV in blood falls, HIV replication continues in lymph nodes. This phase can last anywhere from weeks till more than 13 years.
  3. Third Phase: AIDS related complex refers to many opportunistic infections which affect the patient, like fungal and viral infections such as oral and genital herpes.
  4. Fourth Phase: Development of secondary cancers. Kaposi's sarcoma and non-Hodgkin's lymphoma are common. By this time, there is total loss of cellular immunity.

Mechanism of HIV Infection:

  1. HIV enters the body through body fluid or blood transfusion.
  2. HIV binds with CD4 receptors on the surface of T helper cell.
  3. Both membranes then fuse while the capsid is enzymatically removed to release viral RNA and reverse transcriptase into the cytoplasm of the helper T cell.
  4. Viral RNA undergoes reverse transcription followed by replication to produce a double-stranded viral DNA with the help of enzyme reverse transcriptase.
  5. Reverse transcriptase catalyses the synthesis of second DNA, which is complementary to the first.
  6. Viral DNA enters the nucleus and is incorporated into host DNA, as a provirus.
  7. Provirus may remain dormant but is replicated each time host cell divides.
  8. Activated provirus causes host cell to synthesize huge amounts of viral protein and viral mRNA which are then assembled into new retroviruses.
  9. New retroviruses bud off from host cell membrane, infecting other helper T cells.
  10. Number of helper T cells will gradually decrease and cause risk of individual contacting other diseases and finally leading to death.

Monday, October 3, 2011

Immune Response of Humans.

There are two types of immune response, or rather, what my Bio book tells me so. I was kinda tired of stuffing the facts into my head, so I thought I would type it out here on my iPod Blogger app. :)

Cell-Mediated Immunity:
Cell-Mediated Immune Response
  1. T cells formed in the blood marrow circulate in the blood circulatory system until it reaches the thymus glands.
  2. In thymus glands, T cells differentiate to form T helper cells and T cytotoxic cells, each with a unique type of T cell receptor on its surface.
  3. Mature T helper cell circulates in the blood circulatory system until it reaches an antigen representing cell (APC).
  4. If antigen-MHC complex on APC is complementary with the T cell receptor on the T helper cell, the T cell binds to the APC.
  5. T helper cell that binds with APC secretes interleukin 1.
  6. Interleukin 1 stimulates production of interleukin 2.
  7. Interleukin 2 stimulates the division of T helper cells and T cytotoxic cells to produce clones of effector T helper & effector T cytotoxic cells respectively and memory cells.
  8. Circulating T cytotoxic cells bind with complementary antigen-MHC complex on infected cells.
  9. Effector T cytotoxic cells release perforin that perforated the infected cells to stimulate autolysis.
  10. Effector cytotoxic T cells attacks other infected cells, as infected cell perform autolysis.
  11. Memory T cells respond for a second invasion of the same pathogen by actively dividing to form effector T cells.

Humoral Immune Response:
  1. B cells are formed and mature in bone marrow.
  2. Mature B cells synthesize antibodies, which attach to the 2 tips acting as receptors.
  3. B cells with complimentary antibody phagocytosise the free complimentary antigens encountered.
  4. Antigen is cut into smaller pieces and presented as the antigen-MHC complex on it's plasma membrane.
  5. T helper cell with complimentary T cell receptor binds to antigen-MHC complex.
  6. T helper cell secretes interleukin 2.
  7. Interleukin 2 stimulates B cell to divide and, form clones of effector B cells and memory cells.
  8. Effector B cells produce large quantity of free antibodies with same specific configuration.
  9. Antibodies destroys antigen by precipitation, antitoxins and agglutination.

Interesting how our immune system works, right?
The only problem is, it's only interesting when you need not memorize it for finals!