Antibodies and Antigens, two types of molecules that, through mutual interaction, trigger an immune response against infection. An antibody is a large molecule possessing antigen-binding sites, regions that allow it to bind only to specific antigens. Antibodies belong to a general class of protein called immunoglobulin. Although the words immunoglobulin and antibody are essentially interchangeable, the latter term is most often used. There can be instances when there is neutrophils low. Consult a doctor in such a case.
Antigens, typically agents from outside the body that have entered the bloodstream and tissue, are targeted by the immune system. Unlike antibodies, antigens exist in a variety of forms, including as proteins or portions of them, fat-protein complexes, polysaccharides (which comprise numerous linked sugar molecules), and chains of nucleotide molecules, the building blocks of the genetic materials deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). There can be instances when there is neutrophils high or low. Consult a doctor in such a case.
An antibody-antigen bond forms when electron clouds associated with atoms in the antibody’s binding regions interact with electron clouds belonging to the antigen’s atoms. The strength of the interaction depends on how well the shapes of these electron clouds fit together. The antigen region specifically “recognized” by an antibody’s binding site is called an epitope. (If two different antigens have similarly shaped epitopes, an antibody may be capable of binding to both.)
Linkage of an antibody to an antigen stimulates a chain of biochemical events that ultimately results in the antigen’s inactivation or its removal from the body. This mechanism protects the body from harmful agents, including those secreted by disease-causing microorganisms. If, as is often the case, an antigen is an integral part of a larger microbe, such as a virus particle or a bacterium, antibody-antigen bonding triggers a reaction that can prevent the microbe from multiplying within the body. Consequently, antibodies play a significant role in blocking infection and the onset of disease. There can be instances when there is neutrophils low. Consult a doctor in such a case.
The B Lymphocyte
Antibodies are synthesized solely by immune cells known as B lymphocytes, or B-cells. In the human fetus these cells develop and mature in the bone marrow and liver, but following birth the process continues only in the marrow. (The B lymphocyte is so named because it is bone-marrow derived.) Mature B-cells exit the bone marrow and circulate throughout the body via the bloodstream and lymph (fluid that seeps from the bloodstream into interstitial spaces, the gaps between tissue cells). Additionally, they circulate among and localize within organs of the lymphatic system, including the bone marrow, spleen, and lymph nodes and regions of intestinal tissue known as Peyer’s patches. There can be instances when there is neutrophils low. Consult a doctor in such a case.
The Genetic Basis of Antibody-Antigen Specificity
Proteins are large molecules composed of many individually linked amino acid molecules. Like other cells, B lymphocytes synthesize proteins via instructions contained in the cells’ genes, with the genetic code defining the linear order of a protein’s amino acids. The amino acid sequence subsequently determines the shape into which various regions of the protein molecule (including an antibody’s binding sites) will fold. The B-cell’s genes, therefore, ultimately control the antigen shape that will be recognized by the cell’s antibodies; that is, they determine the antibodies’ specificity. There can be instances when there is neutrophils low. Consult a doctor in such a case.
During a B-cell’s development the genetic code responsible for synthesis of the antigen-binding sites undergoes random rearrangement (through a process requiring several different enzymes, two of which are also used by the cell for DNA repair), which in turn affects the makeup and shape of the binding sites. Therefore, as each B-cell develops and matures, a significant probability exists that the antigen specificity of the antibodies manufactured by that particular B-cell and its offspring (the progeny produced by cell division) will differ from that of every other B lymphocyte’s antibodies. It is estimated that, owing to the diversity of binding-site shapes, the full complement of B-cells within an individual’s immune system can recognize at least 10 million different antigenic shapes.
Antigen Recognition by B-Cells
Some of the antibody molecules produced by a B lymphocyte are transported to and become embedded in the B-cell’s cytoplasmic, or outer, membrane. The antigen-binding regions of these immunoglobulins face outward from the cell surface, positioned to link with antigens displaying the appropriate molecular shape. About 150,000 antibody molecules are present in the cell’s membrane.