Killer T-cells directly kill cells that have already been infected by a foreign invader. T-cells also use cytokines as messenger molecules to send chemical instructions to the rest of the immune system to ramp up its response. Activating T-cells against cancer cells is the basis behind checkpoint inhibitors, a relatively new class of immunotherapy drugs that have recently been federally approved to treat lung cancer, melanoma and other difficult cancers. Cancer cells often evade patrolling T-cells by sending signals that make them seem harmless.
Checkpoint inhibitors disrupt those signals and prompt the T-cells to attack the cancer cells. Researchers are also developing a technology called CART therapy, in which T-cells are engineered to attack specific cancer cells.
This is designed to allow the T-cells to recognize a specific protein on the tumor cells. This technology, also called adoptive cell transfer, is generating excitement among researchers as a potential next-generation immunotherapy treatment. While both are critical to the body's defense against disease and infection , T-cells and B-cells play very different roles. But as their differences and similarities show, both types of immune cells employ important natural defenses in helping the body fight cancer.
Learn why some cancer treatments may damage the immune system. Make a difference in the fight against cancer by donating to cancer research. Healthy red blood cells easily pass through the spleen; however, damaged red blood cells are broken down by macrophages large white blood cells specialized in engulfing and digesting cellular debris, pathogens and other foreign substances in the body in the spleen.
The spleen serves as a storage unit for platelets and white blood cells. The spleen aids the immune system by identifying microorganisms that may cause infection. In addition to the lymph nodes and spleen, mucosal associated lymphoid tissues MALTs and gut associated lymphoid tissues GALTs play a vital role in the immune system, although they are considered to be part of the lymphatic system. MALTs are lymphoid tissues found in parts of the body where mucosa is present, such as the intestines, eyes, nose, skin and mouth.
They contain lymphocytes and macrophages that defend against pathogens attempting to enter from outside the body. Many cells work together as part of the innate non-specific and adaptive specific immune system. Immune cells are sometimes called white blood cells or leukocytes. Figure 2.
Blood Cells. Granulocytes are a type of leukocyte that contain granules in their cytoplasm containing enzymes. Neutrophils, basophils and eosinophils are types of granulocytes. Neutrophils are considered the first responders of the innate immune system. Neutrophils and macrophages circulate though the blood and reside in tissues watching for potential problems.
Cells of the adaptive immune system also called immune effector cells carry out an immune function in response to a stimulus. Natural killer T lymphocytes and B lymphocytes are examples of effector cells. For example, activated T lymphocytes destroy pathogens via cell-mediated response. Activated B cells secrete antibodies that aid in mounting an immune response. Effector cells are involved in the destruction of cancer.
Figure 3. Non-effector cells are antigen-presenting cells APCs , such as dendritic cells, regulatory T cells, tumor-associated macrophages and myeloid-derived suppressor cells. Non-effector cells cannot cause tumor death on their own. Non-effector cells prevent the immune action of the effector cells.
In cancer, non-effector cells allow tumors to grow. Tumor antigens can trigger adaptive immunity. Cells, such as macrophages, dendritic cells and B cells, that can process protein antigens into peptides. These peptides can then be presented along with major histocompatibility complex to T-cell receptors on the surface of the cell.
Figure 4. When the body discovers such a substance several kinds of cells go into action in what is called an immune response. Below is a description of some of the cells that are part of the immune system. Lymphocytes are one of the main types of immune cells. Lymphocytes are divided mainly into B and T cells. Macrophages are the body's first line of defense and have many roles. A macrophage is the first cell to recognize and engulf foreign substances antigens.
Macrophages break down these substances and present the smaller proteins to the T lymphocytes. T cells are programmed to recognize, respond to and remember antigens. This is because class switching occurs during primary responses.
IgG is a monomeric antibody that clears pathogens from the blood and can activate complement proteins although not as well as IgM , taking advantage of its antibacterial activities. Furthermore, this class of antibody is the one that crosses the placenta to protect the developing fetus from disease exits the blood to the interstitial fluid to fight extracellular pathogens.
IgA exists in two forms, a four-chain monomer in the blood and an eight-chain structure, or dimer, in exocrine gland secretions of the mucous membranes, including mucus, saliva, and tears. Thus, dimeric IgA is the only antibody to leave the interior of the body to protect body surfaces. IgE is usually associated with allergies and anaphylaxis. It is present in the lowest concentration in the blood, because its Fc region binds strongly to an IgE-specific Fc receptor on the surfaces of mast cells.
IgE makes mast cell degranulation very specific, such that if a person is allergic to peanuts, there will be peanut-specific IgE bound to his or her mast cells.
In this person, eating peanuts will cause the mast cells to degranulate, sometimes causing severe allergic reactions, including anaphylaxis, a severe, systemic allergic response that can cause death. Clonal selection and expansion work much the same way in B cells as in T cells. Only B cells with appropriate antigen specificity are selected for and expanded. Eventually, the plasma cells secrete antibodies with antigenic specificity identical to those that were on the surfaces of the selected B cells.
Notice in the figure that both plasma cells and memory B cells are generated simultaneously. Figure 2. During a primary B cell immune response, both antibody-secreting plasma cells and memory B cells are produced. These memory cells lead to the differentiation of more plasma cells and memory B cells during secondary responses. Primary and secondary responses as they relate to T cells were discussed earlier. This section will look at these responses with B cells and antibody production.
Because antibodies are easily obtained from blood samples, they are easy to follow and graph Figure 3. As you will see from the figure, the primary response to an antigen representing a pathogen is delayed by several days. This is the time it takes for the B cell clones to expand and differentiate into plasma cells. The level of antibody produced is low, but it is sufficient for immune protection. The second time a person encounters the same antigen, there is no time delay, and the amount of antibody made is much higher.
Thus, the secondary antibody response overwhelms the pathogens quickly and, in most situations, no symptoms are felt. When a different antigen is used, another primary response is made with its low antibody levels and time delay.
Figure 3. Antigen A is given once to generate a primary response and later to generate a secondary response. When a different antigen is given for the first time, a new primary response is made.
Immunity to pathogens, and the ability to control pathogen growth so that damage to the tissues of the body is limited, can be acquired by 1 the active development of an immune response in the infected individual or 2 the passive transfer of immune components from an immune individual to a nonimmune one.
Both active and passive immunity have examples in the natural world and as part of medicine. Active immunity is the resistance to pathogens acquired during an adaptive immune response within an individual. Naturally acquired active immunity, the response to a pathogen, is the focus of this chapter. Artificially acquired active immunity involves the use of vaccines.
A vaccine is a killed or weakened pathogen or its components that, when administered to a healthy individual, leads to the development of immunological memory a weakened primary immune response without causing much in the way of symptoms.
Thus, with the use of vaccines, one can avoid the damage from disease that results from the first exposure to the pathogen, yet reap the benefits of protection from immunological memory. The advent of vaccines was one of the major medical advances of the twentieth century and led to the eradication of smallpox and the control of many infectious diseases, including polio, measles, and whooping cough.
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