B cells and T cells for line of defence Specific Immunity B cells and T cells for line of defence By Tommy Ness, Jaydn McRae & Elijah Costigan

Key Ideas KEY IDEAS If non-specialised defences fail to prevent infection, specialised responses occur. All cells have protein markers on their surfaces. Non-self markers on cells entering a person are called antigens. A number of different kinds of cell are involved in specific immunity. The phenotype is the physical, biochemical or physiological expression of the genotype. Some cells produce antibodies that circulate in body fluids and react with specific antigens.

Quiz What are b cells? a) Bone Cells b) B lymphocyte or plasma cell c) Beta plasma cell d) T Cells

What Is The Function Of A Plasma Cell A) Produce Anitbodies B) Attach To Fallopian Tubes To Bring On Pregnancy C) To Produce Antigens D) Stimulate Production Of a pathogen

Speech The third line of defence in the body, after natural immunity and non-specific, is specific immunity. This is a response by the immune system to a particular antigen. The Heroes of Specific immunity are B and T cells. These are the two main groups of lymphocytes in the body, and as such are also known as B and T lymphocytes. Once immunity is acquired, it is usually long lasting or even for life. This is due to memory cells and is the main focus behind vaccination. Since the immune system has to target foreign cells in the body, a system is need to discover which are self and non-self.

Self And Non-Self Every cell in the body has specific proteins on the surface of their cell membrane which acts as a marker. The proteins are determined by genes, so each person has different markers, and these unique markers make up the major histocompatibility complex, or MHC. This way, every single cell has MHC Markers on their surface; which allows immune cells to distinguish between self and non-self. Self cells will have our MHC marker; whist non-self-antigens will not have a different marker, which will register it as foreign, and an immune response begins. B and T cells are able to distinguish between self and non self cells due to receptors on their membrane. They have receptors that recognise self and non-self markers. As you will learn soon, not every B and T cell has the same receptors to detect non-self MHC markers, because these change from antigen to antigen.

Antigens An antigen is a toxin or other foreign substance that induces an immune response. They have unique shapes, react with specific B and T cells, Stimulate the production of specific antibodies, and are often made of protein, but some are polysaccharides.

B & T Cells B and T cells: B and T cells are both lymphocytes, which are special types of white blood cells. B and T cells are produced in the bone marrow. However, T cells leave the bone marrow before they are fully developed and then travel to the thymus gland. Here is where they differentiate with B lymphocytes to form T lymphocytes, which stands for thymus-dependent. B cells remain in the bone marrow until fully developed. It is the stem cells in bone marrow which create all types of blood cells.

B Cells Have immunoglobulins on their surface. These are proteins designed to detect antigens. Another name for immunoglobulins is antibodies. The immunoglobulin’s on the surface of B cells have a specific structure, and as a result are only able to detect one kind of antigen. However, there are millions of different antigens our body must respond to. When B cells are maturing in the bone marrow, only a few of each kind of B cells is produced, because genetic material undergoes change. This is why there is diversity within B cells. This way, there are now millions of different B cell, with different immunoglobulin’s, with the capability to detect different antigens. The poses a problem however, that there are not enough b cells present to counter an invading pathogen. This is fixed through clonal-selection. The clonal selection hypothesis is a widely accepted model for the way the immune system responds to infection. It also shows how certain B and T lymphocytes respond to specific antigens that are invading the body.

Since for example, the immunoglobulins on the surface of the B cell can only combine with certain antigens, it is likely that an antigen passes by many B cells before it finds one it can combine with. In this sense, the antigen ‘selects’ the B cell that will lead to its death. The selected B cell then reproduces rapidly to give rise to a number of identical B cells. Now there is enough B cells to fight the pathogen. Each of the reproduced cells also rapidly reproduces to form a larger clone of cells. This process is known as clonal expansion. Each of these cells will have the same specific immunoglobulin. Most of these cells with differentiate into plasma cells. These plasma cells will produce the same kind of antibody, which is released into the blood stream or lymph system. The distinction between B cells and plasma cells usually occurs in the lymph nodes. (Mention memory cells here) If more cells are produced than needed, they are normally killed off through apoptosis.

T Cells T cells mature in the thymus. There are many different kinds of T cells which recognise many different antigens. Like B cells, only a few of each kind of T cells are produced, with different immunglobulins on their surface, so that. After encountering a specific antigen, T cells reproduce in the same way as B cells. T memory cells are formed. However, T cell do not make Antibodies. There are different kinds of T cells, and each reacts with a different part of the body. When T cells and phagocytes are involved in immunity it is known as specific immunity. Phagocytes are a type of cell within the body capable of engulfing and absorbing bacteria and other small cells or particles. There are three main types of T cells. T cells themselves, which have receptors on their surface which enable them to recognise non-self markers.

The second is Helper T (Th) cells, these are regulatory cells which stimulate the production of other T and B cells. B cells will not reproduce and form plasma cells without the assistance of Th cells. Th cells also release chemicals which attract other white blood cells to areas containing antigens. Lastly, Cytotoxic T (Tc) cells kill body cells that have been infected by a virus. This is because the infected body cell has foreign antigen MHC markers on its cell membrane/surface as well as class 1 markers. Tc cells kill the infected cell through secreting proteins which punch holes in the membranes of cells, allowing their contents to ooze out. Memory Th cells and Memory Tc cells are made during the initial response to the antigen.  (Expand, including similarities and differences between B and T cells)-mention more on T cells

Difference between Non-specific and specific defense Non-specific defense system are mechanisms such as the skin, the chemicals in our perspiration, saliva, tears, the hairs in our nostrils. These all form physical barriers to protect us against disease. Another example of non-specific defense would be fever, in which we raise our body temperature to inhibit the growth of pathogens. As can be seen, this varies immensely from the specific defense system, since it does not actually target a pathogen, hence the name.

T Cells: A) Do not have the ability to produce other T Cells B) Receptors on their cell membranes that can recognise ‘self’ markers C) On average 30,000 Mitochondria D)Receptors on their cell membranes that can recognise ‘non self’ markers

What Is The Function Of A Plasma Cell A) Produce Anitbodies B) Attach To Fallopian Tubes To Bring On Pregnancy C) To Produce Antigens D) Stimulate Production Of a pathogen

Diagram Of B & T Cell Origin

Diagram Of Stem Cell Development

Clonal selection

Clonal Selection Video http://www.youtube.com/watch?v=ikQJQjomrbE which is the term that describes the growth of bone marrow as not growing spontaneously, but regulated by a factor, the colony stimulating factor

Table of Antibodies Type of antibody IgG IgA IgM IgD IgE approx. concentration in serum 12 2 1 0.04 0.000.02 ability to cross placenta yes no present in saliva and tears present in milk active against viruses some active against some bacteria involved in allergy reactions

Quiz What are b cells? a) Bone Cells b) B lymphocyte or plasma cell c) Beta plasma cell d) T Cells

Bibiliography http://en.wikipedia.org/wiki/Memory_T_cell http://en.wikipedia.org/wiki/Memory_B_cell