Immunology: Group Members

Immunology Group Members Aaliya Blackman Bibi Khan

Content  Definition of “immune response”

 Comparison between the origin and maturation of B- and Tlymphocytes  Describe the mode of action of phagocytes  Distinguish between the humoral and the cell mediated responses

 Explain the role of memory cells in long term immunity

What is is immune What Immuneresponse? Response? This is the body’s response caused by it’s immune system being activated by antigens

Comparison between the origin and maturation of B- and Tlymphocytes The white blood cells that are involved in an acquired immune response are called lymphocytes. There are two types of lymphocytes - B-cells and T-cells. Both of these cells are continually produced in the bone marrow. These cells are not involved in the immune response until they are fully developed. The B-cells mature in the bone marrow, while T-cells migrate through the bloodstream and mature in the thymus gland. B-cells help fight against bacteria and viruses that enter the body. They are able to detect and bind to specific foreign invaders (antigens) that enter the body. This triggers other immune cells to destroy the antigen. Naive Bcells are B-cells that have not encountered an antigen yet. Once a B-cell has been exposed to an antigen, it is called a plasma cell. The first step of B cell maturation is an assessment of the functionality of their antigen-binding receptors. This occurs through positive selection for B cells with normal functional receptors. A mechanism of negative selection is then used to eliminate self-reacting B cells and minimize the risk of autoimmunity. Negative selection of selfreacting B cells can involve elimination by apoptosis, editing or modification of the receptors so they are no longer self-reactive, or induction of energy in the B cell. Immature B cells that pass the selection in the bone marrow then travel to the spleen for their final stages of maturation. There they become naïve mature B cells, i.e., mature B cells that have not yet been activated.

T cell, also called T lymphocyte, type of leukocyte (white blood cell) that is an essential part of the immune system. T cells are one of two primary types of lymphocytes—B cells being the second type—that determine the specificity of immune response to antigens (foreign substances) in the body. They are two main type of T cells: Helper T-cells and Killer T-cells  Helper T- cells stimulates B cells to make anti-bodies and help Killer cells develop  Killer T-cells directly kill cells that have already been infected by a foreign invader(antigen) Maturation of T- Cells T cells all originate from cells in the bone marrow that divide by mitosis. As a child grows and develops, these immature T-cells move to the thymus gland in the neck, where they divide to form a large population of T-cells As the T-cells mature, they begin to produce glycoproteins called CD4 and CD8. These glycoproteins are placed in their plasma membranes, where they act as receptors. Each cell then stops producing one of these types of glycoprotein, and becomes either a CD4 plus cell( producing CD4 only) or a CD8 plus cell (producing CD8 only). During their development in the thymus gland, only T cells that have a set of receptors enabling them to bind to the proteins antigens on the body’s own cells ( called the MHC complex) are allowed to survive. Moreover, any that interact with the MHC complex too strongly are also destroyed. This ensures that all of the T- cells that remain in the body’s own cells, and will not initiate auto-immune reactions in which they attack and harm them. Overall, only about 2% of all the T-cells that develop in the thymus gland pass these tests and survive.

Describe the mode of action of phagocytes They are two of white blood cells (Phagocytes) known as:  Neutrophils  Macrophages Neutrophils: are found in the blood, where they make up about 60% of the white blood cells Macrophages: a large phagocytic cell found in stationary form in the tissues or as a mobile white blood cell, especially at sites of infection

Phagocytes: are known for their actin process, as they engulf the whole foreign or harmful substances or cells. The plasma cells disappear after the immune response work is over, but again the memory B-cells remain active for a long time so that the invader may not be able to attack the body and its immune system again as antibodies are already present for them to fight and eradicate them.

Phagocytosis, process by which certain living cells called phagocytes ingest or engulf other cells or particles. The phagocyte may be a free-living one-celled organism, such as an amoeba, or one of the body cells, such as a white blood cell. In some forms of animal life, such as amoebas and sponges, phagocytosis is a means of feeding. In higher animals phagocytosis is chiefly a defensive reaction against infection and invasion of the body by foreign substances (antigens). Before phagocytosis is accomplished, the phagocyte and the particle must adhere to each other, the possibility of which depends largely on the chemical nature of the surface of the particle. In the case of bacteria, if the phagocyte cannot adhere directly, protein components of the blood known as opsonins (e.g., complement and antibodies) form a surface film on bacteria—a process known as opsonization. Phagocytes adhere to the opsonins, and phagocytosis follows. Encapsulated bacteria are ingested with more difficulty. In the absence of specific antibodies that recognize the bacteria, opsonization cannot occur, and the bacteria repel phagocytes. The surfaces of such bacteria are coated with special antibodies only after the body has mounted an immune response to the presence of that particular kind of bacterium. Such antibodies are of great importance in establishing immunity to diseases.

The speed with which a phagocytic cell ingests a particle varies somewhat with the size of the particle. Small particles, such as bacteria or minute grains of charcoal, are ingested almost instantaneously. Larger objects, such as clumps of bacteria or tissue cells, are phagocytosed over the course of a more-prolonged response. The cell flows around the object until it has been completely engulfed. The engulfed object is thus enclosed within a membrane-bound vacuole called a phagosome. The phagocyte digests the ingested particle with hydrolytic enzymes, which are contained within membrane-enclosed sacs called lysosomes found within the cell. Phagocytic enzymes are secreted into the vacuole in which digestion takes place. Small organic components of the particle are used to build larger molecules needed by the cell.

 Both systems are active immunities.  Both systems have immunological

Similarities of the Humoral and Cell Mediated Responses

memory present.

 Both systems are ineffective in immune deficient individuals.

 Both systems are effective against a wide variety of microbial pathogen

Differences Cell mediated Response

 It is mediated by T-cells.  Antibodies are not formed.  Receptors are used to detect antigens.  T-cell receptors binds to the T-cells which binds to the antigens them self.  Protects against intracellular bacterial pathogens (eg: viruses,

Humoral (antibody) Response

 It is meditated by antibodies (produced by B-cells).  Antibodies are formed.  Antibodies are used to detect antigens  B-cells produce anti-bodies and the anti-bodies binds to the antigens.  Protects against extracellular bacterial and viral pathogens.

Roles of memory cells in long term immunity Memory cells record information for your immune system about how to fight and destroy viruses and the like that plague the body. When a disease strikes the body the memory cells instruct the body on how to produce antibodies. Once created, these antibodies are released into the bloodstream. Then the antibodies find the disease and destroy it. If a disease that was not previously encountered is introduced into the body, then the immune system (hopefully) destroys it and the memory cells record how it was done.

The End!