Tuesday, March 29, 2011

Intruders Beware

An intruder enters, and suddenly it is met by a force that begins the fight. After time, backups arrive to fight until the end. This may sound like the plot of an action or war movie, but really I am talking about the body’s immune system. The initial troops are known as the innate immunity and the ones that come in later are the adaptive immunity. The innate immunity can consist of the physical barriers, such as the skin and mucous membranes. It also involves the secretion of chemical signal, fever, and inflammatory response. The innate immunity is supposes to prevent entry and spread of invaders throughout the body.

The more complex system of immunity is the adaptive immunity. We can call the adaptive immunity, the special force for fighting infection. Once the body is exposed, it reacts by activating B and T cells. The T-cells are a part of the cell-mediated immunity and the B cells are a part of humoral immunity. The humoral immune response is mediated by the release of antibodies. Antibodies are also known as immunoglobulins and have a Y shape that consists of two large heavy chains and two smaller light chains. The antibody has a specific binding site for the antigen or intruder. Once the intruder is bound to the antibody, it is destroyed on-site or is marked for later destruction.

The antibody is specific to its target and since new mutations of bacteria and viruses come around every day, how is the body able to adapt to making so many different antibodies when the genome is so small? A person can produce a million different antibodies and the way we can do this is through DNA rearrangement followed by alternative splicing of the RNA transcript. Let us first discover the marvels of DNA rearrangement. DNA rearrangement is gene reorganization. Gene segments containing information about the formation of antibodies come together and are assembled during the formation of B cells. DNA rearrangement brings together and assembles the antibody coding segments. The different arrangements of the segments allow for many forms of a protein from a small group of genes. The diversity of the B cell formation lies in the formation of the heavy and light chains of the antibody by using variable combinations of genes. In the light chain, DNA rearrangement combines three separated genes to code for one polypeptide. In the heavy chain, four genes are shuffled around by DNA rearrangement to produce the polypeptide. Another factor that affects the variability in antibodies is alternative splicing. Once DNA is transcribed into RNA, there are modifications that must be made. One of the changes is cutting out the introns and exons. This can occur by not cutting out an intron that normally would have been removed or by changing the arrangement, in which the exons are joined after the introns are removed. This allows for variation is coding during translation, leading to new forms of a protein. The process of producing antibodies is complex, but it allows our immune system to hone its skills for fighting intruders.

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