The complement system attacks the surface of pathogens. Containing over 20 proteins, the complement system is the biggest humoral component of the innate immune response. This response is triggered by complement binding to antibodies attached to carbohydrates on the surface of microbes triggering the rapid killing response. The complement proteins are initially bound to microbes and activate their protease activity which activates other complement proteases producing a catalytic cascade that amplifies the inial signal using positive feedback. This results in the production of peptides attracting immune cells and increasing the cascular permeability while marking the surface of the pathogen for destruction.
Another quick response to infection is inflammation. Usually marked by redness and swelling caused by increased blood flow to the tissue, inflammation is produce by eicosanoids and cytokins that are released by attacked cells. Eicosanoids induce fever and dilation of blood vessels while leukotrienes attract white blood cells. Cytokins recruit immune cells to the infection site to promote healing of damaged tissue after removing the pathogens.
The adaptive immune system proves to eliminate and prevent pathogens by recognizing and remembering specific pathogens and creating stronger attacks for each encounter of the pathogen. This adaptive property helps prepare the body for future challenges.
When an antigen binds to this immunoglobin, the B cell engulfs the anibody-antigen complex and degrades it. Following this process, the T cells stimulate the B cells to proliferate and the process is repeated for additional antigens. B cells may live for several days; some B cells live for years and are called memory B cells. These can stimulate a more rapid response to an antigen they have encountered in the past.
Antibody structures form a related and big group of proteins. All immunoglobins contain four subunits at the least: 2 identical heavy chains (weighing 53-75 kD) and 2 identical light chains (weighing approximately 23 kD). The subunits are attached by disulfide bonds as well as non-covalent interactions to form a Y shaped structure which is symmetric. There are five different classes of immunoglobins (IgA, IgD, IgE, IgG, IgM) differing mostly in the type of heavy chain they contain and sometimes in their subunit structure. As a result, different immunoglobins have different functions. For example, IgE bids to allergens and protects against parasitic worms while IgA is found in mucus and prevents colonization. The most common of th immunoglobins by far is IgG.
An immunoglobin consists of homology units which all have the same characteristic fold. This fold, which is in the light chain, consists of a 'sandwich'-like structure composed of three and four stranded anti-parallel beta-sheets that are linked by a disulfide bond. This structure can accommodate an enormous variety of antigens. The light chain recognizes antigens through three loops in its variable domain (which is an area part of the light chain). This domain includes the most amino acid variation among antibodies in the whole immunoglobin; these are called hybervariable sequences.
The forces and bonding involved between an antibody and antigen include van der waals, hydrogen bonding, hydrophobic, and ionic interactions. The two are structurally complementary to each other; therefore, strong bonds are formed. Dissociation constants between an antigen and an antibody range from 10^-4 - 10^-10, which is greater than or equal to the dissociation constant associated with an enzyme and its substrate.
For the most part, immunoglobins are divalent molecules capable of binding to two different antigens at the same time. A foreign organism or substance usually has many antigens on its surface. Thus, a typical immune response consists of a mixture of antibodies with different specificities divalently binding to the antigens. This binding allows the cross-linking of the antigens to form an extended lattice formation, which assists and decreases the time in which it takes to remove the antigen. This also triggers further B cell formation and proliferation. [[Media:Media:Example.ogg]]
An antigen does not influence a B cell to produce new immunoglobin to bind to. Instead, an antigen stimulates the proliferation of a pre-existing B cell antibodies that recognize the antigen. Thus, the immune system has the ability to generate a plethora of different antibodies. Most of these are sufficient for a person to respond through his or her immune system to respond to almost any antigen he or she may encounter. The diversity in antibody sequences arises from genetic changes during B lymphocyte development not only from the number of immunoglobin genes.
The immune system is unique in that it only responds to foreign substances and not to the high and diverse amount of endogenous molecules.Because most macromolecules are virtually antigenic, transferring tissues, organs, or blood samples among individuals and within species presents great challenges and is being researched continuously.
The immune system may lose tolerance to some of its self-antigens, causing an autoimmune disease, which at its worst, could be deadly. Autoimmune diseases include: Addison's disease, Crohn's disease, Multiple sclerosis, Psoriasis, and Graves' disease.
Addison's disease is caused when the adrenal glands do not produce enough steroid hormones known as cortisol. This rare genetic disease may develop in children, adults, and even some species of animals. The treatment involves the replacement of hormones.
Crohn's disease is the autoimmune, inflammatory disease of the intestines. The body's immune system attacks the gastrointestinal tract causing inflammation. Commonly believed to be a primary T cell autoimmune disorder, new studies believe it to be an impaired innate immunity due to impaired cytokine secretion by macrophages causing microbial-induced inflammatory response.
Multiple sclerosis is when the body's immune system attacks the central nervous system leading to demyelination. Affecting the communication between the spinal cord and the brain, nerve cells communicate by sending electrical signals (action potentials) down axons which are wrapped in myelin. Myelin is attacked and is damaged resulting in MS.