The human immune system is a truly amazing constellation of responses to attacks from outside the body. It has many facets, a number of which can change to optimize the response to these unwanted intrusions. The system is remarkably effective, most of the time. This note will give you a brief outline of some of the processes involved.

* An "antigen" is any substance that elicits an immune response, from a virus to a sliver *

The immune system has a series of dual natures, the most important of which is self/non-self recognition. The others are: general/specific, natural/adaptive - innate/acquired, cell-mediated/humoral, active/passive, primary/secondary. Parts of the immune system are antigen-specific (they recognize and act against particular antigens), systemic (not confined to the initial infection site, but work throughout the body), and have memory (recognize and mount an even stronger attack to the same antigen the next time).

Self/non-self recognition is achieved by having every cell display a marker based on the major histocompatibility complex (MHC). Any cell not displaying this marker is treated as non-self and attacked. The process is so effective that undigested proteins are treated as antigens.

Sometimes the process breaks down and the immune system attacks self-cells. This is the case of autoimmune diseases like multiple sclerosis, systemic lupus erythematosus, and some forms of arthritis and diabetes. There are cases where the immune response to innocuous substances is inappropriate. This is the case of allergies and the simple substance that elicits the response is called an "allergen".

Fluid System of the body :

There are two main fluid systems in the body: blood and lymph. The blood and lymph systems are intertwined throughout the body and they are responsible for transporting the agents of the immune system.

The Blood System :

Blood constitutes about 7% of the body's total weight. The blood flows from the heart into arteries, then to capillaries, and returns to the heart through veins. All blood cells are manufactured by stem cells, which live mainly in the bone marrow, via a process called hematopoiesis. The stem cells produce hemocytoblasts that differentiate into the precursors for all the different types of blood cells. Hemocytoblasts mature into three types of blood cells: erythrocytes (red blood cells or RBCs), leukocytes (white blood cells or WBCs), and thrombocytes (platelets).

The Lymph System :

Lymph is an alkaline (pH > 7.0) fluid that is usually clear, transparent, and colorless. It flows in the lymphatic vessels and bathes tissues and organs in its protective covering. There are no RBCs in lymph and it has a lower protein content than blood. Like blood, it is slightly heavier than water.

Lymph carries lipids and lipid-soluble vitamins absorbed from the gastrointestinal (GI) tract. Since there is no active pump in the lymph system, there is no back-pressure produced. The lymphatic vessels, like veins, have one-way valves that prevent backflow. Additionally, along these vessels there are small bean-shaped lymph nodes that serve as filters of the lymphatic fluid. It is in the lymph nodes where antigen is usually presented to the immune system.

The Lymphoid System :

Lymph nodes are small bean shaped structures lying along the course of lymphatics. They are aggregated in particular sites such as the neck, axillae, groins and para-aortic region. Lymph nodes have two main functions:
1) - phagocytic cells act as filters for particulate matter and micro-organisms
2) - antigen is presented to the immune system
Lymph nodes are the filters along the lymphatic system. Their job is to filter out and trap bacteria, viruses, cancer cells, and other unwanted substances, and to make sure they are safely eliminated from the body.

B Cells : The major function of B lymphocytes is the production of antibodies in response to foreign proteins of bacteria, viruses, and tumor cells. Antibodies are specialized proteins that specifically recognize and bind to one particular protein that specifically recognize and bind to one particular protein. Antibody production and binding to a foreign substance or antigen, often is critical as a means of signaling other cells to engulf, kill or remove that substance from the body.

These enter the lymph node via HEVs and pass to the follicles. If activated by antigenic stimulation they proliferate and remain in the node. Unstimulated B cells, however, pass out rapidly from the node to return to the general circulation. Activated B cells within the lymphoid follicles are known as follicle centre cells. The pale staining central area of a secondary follicle is known as a germinal centre and this is surrounded by a mantle zone consisting of small, naive B cells and a few T cells. The follicle centre cells within the germinal centres consist of cells with cleaved nuclei (centrocytes) and cells with larger more open nuclei and several nucleoli (centroblasts). Stimulated mature B cells responding to antigen change into centrocytes and then centroblasts. The centroblasts leave the follicle and pass to the paracortex and medullary sinuses, where they become immunoblasts. The immunoblasts divide to give rise to plasma cells or memory B cells which are ready for their next encounter with specific antigen. ** When weakened by the overuse of antibiotics and other chemicals, the immune system ceases to operate in such an efficient manner and the result is illness, disease, allergies ect... ** - LRU

Lymphocytes alone are not to make an effective immune response. They are assisted by so-called accessory cells. The paracortex contains lymphocytes and accessory cells along with supporting cells and it is the predominant site for T lymphocytes within the lymph node.

T Cells : The various types of T cell enter the node from the blood via the HEVs. When activated they form lymphoblasts which divide to produce a clone of T cells responding to a specific antigen. Activated T cells then pass into the circulation to reach peripheral sites. Lymphocytes recirculate between lymphoid and non-lymphoid tissues. This helps in allowing lymphocytes to be exposed to the antigens which they recognise and is, therefore, valuable in the distribution of effector cells of the immune response to the sites where they are needed. The recirculation is a complex process depending on interactions between the cells of the immune response and other cell types.

T lymphocytes are usually divided into two major subsets that are functionally and phenotypically (identifiably) different. The T helper, and the T killer/suppressor subset. The main function of the T helper cell is to augment or potentiate immune responses by the secretion of specialized factors that activate other white blood cells to fight off infection. The T killer cells are important in directly killing certain tumor cells, viral-infected cells and sometimes parasites. Both types of T cells can be found throughout the body. They often depend on the secondary lymphoid organs (the lymph nodes and spleen) as sites where activation occurs, but they are also found in other tissues of the body, most conspicuously the liver, lung, blood, and intestinal and reproductive tracts.

Lymph Cleansing :

The lymphatic system includes lymph vessels and nodes, thymus gland, tonsils and spleen. It's really a network of tubing that drains waste products from tissues, produces disease-fighting white blood cells (lymphocytes) and antibodies, and carries the bulk of the body's waste from the cells to the final elimination organs. Special filtering lymph nodes remove infective organisms, so your lymph system is also a key to your body's immune defenses.

Liver health is a key to lymphatic health. The liver produces the majority of lymph, and lymph a major route for nutrients from the liver. The integrity of the lymph system is dependent on immune cells in the liver that filter out harmful bacteria and destructive yeasts.

The spleen is the largest mass of lymphatic tissue. It destroys worn-out red blood cells, and serves as a healthy blood reservoir for fresh red blood. During times of high demand, such as hemorrhage, the spleen can release its stored blood and prevent shock from occurring.

Here's an amazing fact : The valves of the lymph system move the waste-filled fluids to be flushed and filtered. But since there is no pump as there is with the heart, lymph circulation depends solely upon your breathing and muscle movement. Physical exercise and diaphragmatic deep breathing are critical to lymph cleansing and to healthy immune response.