Immune System-Part II
The immune system is composed of a very complex network of organs, cells, and molecules. All of these contributors play a significant role in the maintaining the body’s homeostasis. There are two paths the immune system can take. These are known as innate and adaptive immunity. They work in conjunction with one another to provide the proper response to environmental factors. Innate immunity is characterized by a rapid response to the stimulus. It is known as the body’s first line of defense.
As mentioned above, there are several components of the immune system. Notable cellular components are recognized as T and B lymphocytes. To explain a little about their origin, it begins in the bone marrow. Previous to the bone marrow, the T and B lymphocytes start out as stem cells in the bone marrow. These pluripotent stem cells give rise to ...view middle of the document...
The specificity of the antigen binding is defined by the variable domain of the antibody. The variable domain consists of heavy and light chains of immunoglobulins. Each immunoglobulin is formed from gene segments that rearrange into a specific chain to constitute the complete chain. Each molecule of immunoglobulin is formed by two heavy chains and two light chains that are linked by disulfide bonds. There are five types of heavy chains. The heavy chain is also known as the constant domain of the immunoglobulin, which is expressed on the surface as a pre-B cell receptor. Each B lymphocyte presents a single type of light chain associated with the heavy chain. Expression of a complete IgM on the surface of the B lymphocyte leads to maturation progression.
The B lymphocytes are responsible for humoral immunity, which is associated with antibodies. Humoral immunity involves the production and release of antibodies that are capable of neutralizing and destroying antigens. In order to do this, the B cells must go through the process of activation. This results in proliferation of B cells and production of antibodies with high affinity for the antigen that initiated the original immune response. In order for activation to take place, the B cell receptor must bind to the antigen epitope. This event triggers a number of sequential intracellular events to occur. The B cells also act as antigen presenting cells after the antigen is bound to the surface of the B cell receptor. The interacting of MHC (Major Histocompatibility Complex) Class II and a T helper cell initiates a chain of events that lead to expansion and production of cytokines that stimulate proliferation and differentiation of B cells. Complement also plays a role in humoral immunity in that secondary activation signals are expressed on the surface of B cells. The binding of complement factors initiates a signaling cascade that generates a much higher response when compared to those not bound to complement factors.