The Immune System

The immune system is a system within all vertebrates (animals with a backbone) which in general terms, is comprised of two important cell types: the B-cell and the T-cell. The B-cell is responsible for the production of antibodies (proteins which can bind to specific molecular shapes), and the T-cell (two types) is responsible either for helping the B-cell to make antibodies, or for the killing of damaged or "different" cells (all foreign cells except bacteria) within the body. The two main types of T-cells are the "helper"T-cell and the cytotoxic T-cell. The T-helper population is further divided into those which help B-cells (Th2) and those which help cytotoxic T-cells (Th1). Therefore, in order for a B-cell to do its job requires the biochemical help of Th2 helper T-cells; and, for a cytotoxic T-cell to be able to eliminate a damaged cell (say, a virally-infected cell), requires the biochemical help of a Th1 helper T-cell.

Whenever any foreign substance or agent enters our body, the immune system is activated. Both B- and T-cell members respond to the threat, which eventually results in the elimination of the substance or agent from our bodies. If the agent which gains entry is the kind which remains outside of our cells all of the time (extracellular pathogen), or much of the time (virus often released) the "best" response is the production by B-cells of antibodies which circulate all around the body in the bloodstream, and eventually bind to the agent. There are mechanisms available which are very good at destroying anything which has an antibody bound to it. On the other hand, if the agent is one which goes inside one of our cells and remains there most of the time (intracellular pathogens like viruses or certain bacteria which require the inside of one of our cells in order to live), the "best" response is the activation of cytotoxic T-cells (circulate in the bloodstream and lymph), which eliminate the agent through killing of the cell which contains the agent (agent is otherwise "hidden"). Both of these kinds of responses (B-cell or cytotoxic T-cell) of course require specific helper T-cell biochemical information as described above.

Usually, both B-cell and cytotoxic T-cell responses occur against intracellular agents which provides a two-pronged attack. Normally, these actions are wonderfully protective of us. The effect of HIV on the immune system is the result of a gradual (usually) elimination of the Th1 and Th2 helper T-cell sub-populations.

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About T4 Cell

Figure above show T-lymphocyte of human

What is T4 cell?

T4 cell is a helper T cell that displays the CD4 molecule on their surface protein. It’s called as T4 lymphocyte. They also have on their surface, epitope receptors called T-cell receptors (TCRs) that, in cooperation with the CD4 molecules, have a shape capable of recognizing peptides from exogenous antigens bound to MHC-II molecules on the surface of antigen-presenting cells (APCs) and B-lymphocytes. The TCR recognizes the peptide while the CD4 molecule recognizes the MHC-II molecule.

*T-CELL RECEPTOR: The receptor on the surface of T-lymphocytes that bind corresponding peptide epitopes of protein antigens bound to MHC molecules.

*CD MOLECULE: Cluster of Differentiation molecules are molecules serving as phenotypic markers for characterizing and distinguishing leukocyte subsets and functions. For example, CD4 molecules are found on the surface T4-lymphocytes and play a role in immune recognition.

*ANTIGENS: Antigens that enter from outside the body, such as bacteria, fungi, protozoa, and free viruses.

*MHC-II MOLECULES: Class II HLA molecules are made primarily by antigen-presenting cells (APCs, eg, macrophages and dendritic cells) and B-lymphocytes. They bind peptide epitopes from exogenous antigens to enable immune recognition by T4-lymphocytes.

*ANTIGEN-PRESENTING CELL (APC): APCs include dendritic cells, macrophages, and B-lymphocytes. APCs engulf and degrade protein antigens into peptide epitopes, bind those epitopes to MHC molecules, and place them on their surface where they can be recognized by the T-cell receptors of T-lymphocytes.

*B-LYMPHOCYTES:White blood cells that mediate humoral immunity (the production of antibody molecules). B-lymphocytes recognize epitopes of antigens by way of antibody molecules called sIg present on their surface and, after activation, eventually differentiate into antibody-secreting plasma cells.

What is HIV?

The Human Immunodeficiency Virus (HIV) is the virus that leads to AIDS. HIV belongs to a subset of retroviruses called lentiviruses (or slow viruses), which means that there is an interval -- sometimes years -- between the initial infection and the onset of symptoms. HIV is less than 0.2 um in diameter.

Previous names for the HIV include human T-lymphotropic virus-III (HTLV-III), lymphadenopathy-associated virus (LAV), or AIDS-associated retrovirusARV).

Upon entering the bloodstream -- through mucous membranes or blood-to-blood contact -- HIV infects the CD4+T cells and begins to replicate rapidly.

HIV enters the body, and begins to disable the body's immune system by using the body's aggressive immune responses to the virus to infect, replicate and kill immune system cells. Gradual deterioration of immune function and eventual destruction of lymphoid and immunologic organs is central to triggering the immunosuppression that leads to AIDS.

Timeline of AIDS

• 1981 Gay Cancer
• 1982 Haitians Hemophyliacs
• 1983 AIDS Prejudice
• 1984 Virus
• 1985 Rock Hudson, Saliva OK
• 1986 T-Cells AZT
• 1987 Reagan
• 1988 Macrophages
• 1989 Going Public. 27,408 deaths
• 1990 Ryan White, Condoms in School
• 1991 Sex Drugs & Aids, Magic Johnson
• 1992 Arthur Ashe
• 1993 Needles, AZT resistance
• 1994 Losing Ground? 49,311 deaths
• 1995 #1 killer of young adults
• 1996 Cycle of Destruction. 37, 359 deaths
• 1997 CCR5, Cocktails
• 1998 Death Rates, Plunge Cocktail Side Effects
• 1999 New Directions, New Frustrations
• 2000 China
• 2001 Free care in Botswana

The AIDS Epidemic in group:
• 1981-1987
• 1988-1990
• 1991-1993
• 1994-1997
• 1998-1999
• 2000
• 2001