Lymph, Interstitial Fluid and the Lymphatic System
The lymph is the fluid in the lymphatic vessels, which is formed when interstitial fluid from around the cells and tissue structures infiltrates into the vessels in order to circulate out of the various body parts. It contains proteins and other components that enrich the cells. It also drains the body of various wastes and infectious organisms. The interstitial fluid is the fluid that surrounds all body cells, formed from blood serum infiltrating through blood vessel walls. The lymphatic system involves the circulation of lymph throughout the body, just like blood. It is composed of the lymphatic vessels and the lymph nodes. Its roles are the maintenance of fluid homeostasis, immune function, and absorption of lipids.
Lymphoid organs
Lymph nodes are small bean-shaped structures in the lymphatic vessels that filter the lymph as it moves around the body. They contain lymphocytes and are very functional in the immune mechanisms. The bone marrow and the thymus are primary lymphoid tissues as they are involved in the production and development of lymphocytes that are found in the lymph nodes, and which fight infections. The spleen is found on the upper left side of the belly, and its primary role is to filter blood and balance fluid levels in the blood and in the lymphatic system. Tonsils are clusters of lymph nodes in the pharynx. They filter bacteria that get into the body through the mouth or nose. Nodule aggregates are a small localized collection of lymphoid tissue. Lymphatic nodules comprise of the Peyer's patches in the small intestines and tonsils. Both are very active in immune monitoring in the digestive tract.
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The immune system
The immune system is composed of the innate and adaptive immune system (cell-mediated and humoral). The innate immune system leads to an immediate response to an infection, such as inflammation, whereas the adaptive system takes lag time and leads to the creation of immunological memory. It is specific, versatile, memory capable and able to distinguish self from an alien. It is composed of various components and primarily protects the body for infections.
Innate and Adaptive Immunity
Innate immunity is a more spontaneous reaction to an infection, which is activated by the chemical properties of the antigen. It is very independent of the specificity of the antigen. Adaptive immunity on the other had is antigen-specific, slower in response and can memorize the antigen for future immune responses. Adaptive immunity is antigen-specific and is driven by the B and T Lymphocytes only.
Cellular Immunity and T Cells
Cellular immunity involves the activation of phagocytes, antigen sensitive lymphocytes, cytokines and chemokines by various players in the immune system in response to an antigen. It is the most specific and effective immune response, protecting the body against cells that have been infected with viruses, intracellular bacteria, protozoa, and even cancerous cells. The same system is involved in the rejection of transplanted cells. T-cells are activated when presented with MHC Class II molecules on the surface of Antigen-Presenting Cells. Their role is specifically limited to attacking and destroying any infected, cancerous or foreign cells in the body.
Humoral Immunity, B-Cells, and antibodies
Adaptive or humoral immunity is dependent on the B-Lymphocytes. When activated by the Helper T cells, they produce antibodies that attach themselves to the foreign antigen, facilitating their elimination by the phagocytes such as neutrophils. This system deals with freely circulating antigen or those that are temporarily outside cells. Antibodies assist in antigen recognition.
Primary and Secondary Immune Responses
The primary immune response occurs when the immune system of a person comes into contact with a certain pathogen for the first time. There are no specific B-cells or antibodies present to attack the antigen. Once this occurs, humoral immunity against that particular pathogen occurs. A secondary immune response occurs when the pathogen enters the body a second time. By then, antibodies have already been formed, and the pathogen can be easily recognized and attacked by the antibodies as consequently, the phagocytes can trail it. Immunization utilizes a secondary response.
Active and Passive Immunity
Active immunity occurs when the body is exposed to an antigen from a specific pathogen, thereby developing its own antibodies against it on its own. The antibodies come from the body. On the contrary, passive immunity occurs when antibodies against a certain antigen are introduced into the body from a different place, where they have already been developed. This includes antidotes and the antibodies in breast milk.
Types of Immunoglobulins
There are five classes of immunoglobulins. IgA accounts for 15% of all antibodies in the human body. It is found in a variety of body secretions such as milk, saliva, tears, and mucus. IgD has two epitopes binding site and is the second rarest of all antibodies, making up only 0.2%. It is mainly a cell surface receptor on B-Lymphocytes. IgE is very vital in the immune system, yet it is the rarest immunoglobulin, accounting for about 0.002 of all immunoglobulins in the blood. It has a short life of 2 days only and is bound on mast cells or basophils. Its main role is activating of allergic reactions. IgG is the most dominant immunoglobulin in the body, accounting for about 85%. It chiefly circulates in the blood and lymph. It can cross the placental barrier as well. Its main role is enhancing phagocytosis in macrophages and neutrophils. IgM is a pentamer with five monomers and accounts for 13-15% of serum antibodies. It is the first responder to invasion, causing antigen agglutination and can also activate the complement-protein pathway.
Immune disorders
An allergic reaction is a hypersensitive reaction to an antigen that is typically not harmful to the body. These can include some food, pollen or pet dander, but the body considers them to be a threat. Psoriasis is an autoimmune condition, where the life cycle of skin cells is sped up, causing a build-up of cells on the skin surface, scales and red patches that are painful. It is a chronic disease. Lastly, Rheumatoid Arthritis is a progressive autoimmune disease that causes inflammation and pain in various body joints, especially for elderly people. Even though it mainly affects the hands and feet first, it can attack any joint in the body. There are remedies, but it is not curable.
