Cell Recognition

Lymphocytes are able to recognize pathogens, non-self materials (eg cells from a different organism of the same species), toxins, and abnormal body cells such as cancer cells.

Cells can recognize each other via identifying molecules on their cell surface membranes. These molecules have specific 3D structures which may or may not be complementary to identifying molecules on other cells.

Proteins are able to form highly specific shapes due to their tertiary and quaternary structures. They can therefore form many different shapes and allow for detailed differentiation in cell recognition.

Transplanted organs have different identifying molecules, or antigens, on their cell surface to self-cells, identifying them as foreign material. When the immune system identifies these foreign cells it attacks the transplant in the same way it would a pathogen.

Doctors will try to ‘match’ organ donors closely with patients so that their cells are as similar as possible, usually taking organs from relatives, as they are genetically related. Doctors will also prescribe immunosuppressants to prevent the immune system from attacking the transplanted organ.

Membrane carbohydrates are molecules found on the cell surface membrane, where carbohydrates are covalently linked to molecules in the cell membrane to form identifying molecules or receptors.

Glycoproteins are molecules made up of a carbohydrate covalently bonded to a protein. These molecules are involved in cell recognition.

An example of a glycoprotein is the CD4 receptor found on helper T cells.

Glycolipids are molecules made up of a carbohydrate covalently bonded to a lipid. The bond in this molecule is called a glycosidic bond. These molecules are involved in cell recognition.

The most common type of membrane carbohydrate is glycoproteins. Most of the proteins in the cell membrane are linked to a carbohydrate.

Specific defense mechanisms in the body are the action of T lymphocytes in the cellular response and B lymphocytes in the humoral response.

In the fetus, lymphocytes only collide with self-material. Any lymphocytes that fit the antigens of self-material either die or are suppressed, so only lymphocytes that respond to non-self material are matured and present in the body. This is also the same for B cells in the bone marrow, where any cells that show an immune response against self-antigens undergo programmed cell death.

Antigen-presenting cells are cells that display foreign antigens on their cell surface.

An example of an antigen-presenting cell is a phagocyte.

T cells only respond to antigens that are presented on a body cell, such as on antigen-presenting phagocytes or infected body cells.

An antibody is a protein, specifically an immunoglobulin or globular glycoprotein.

Antibodies are synthesized by B cells and plasma cells in the humoral immune response. They are synthesized in response to the presence of non-self material in the body, such as a pathogen or pollen.

An antibody is made up of four chains, two shorter light chains ad two longer heavy chains. These chains are connected by disulfide bridges. The variable region of the antibody is found at the top of the Y shape, and the constant region is found at the button of the Y shape.

The antigen-binding site is found at the two ends of the antibody’s Y shape, at the end of the variable region. The antigen-binding site is located at the ends of both the light and the heavy chains.

The constant region is called constant because it is the same on every antibody, while the variable region is called variable because it has a specific shape that changes depending on the cell that has produced it.

Agglutination is when antibodies bind to multiple antigens, causing non-self cells or particles to clump together in one place. This makes it easier for phagocytes to engulf and destroy foreign material as they are all in one centralized place.

Antibodies can neutralize some toxins by binding to them. This forms an antibody-toxin complex.

The antigen-antibody complex is the name given to when an antibody binds to a specific complementary antigen.

Antibodies can act as chemical markers which stimulate phagocytes to move towards them and the agglutinated antigens.

Antibodies have two antigen-binding sites rather than one. This means antibodies can attach to two antigens at once, so can hold two cells or particles together at once.

Monoclonal antibodies are a specific, single type of antibody, where all antibodies are identical to one another. This is because they are clones of one another and are produced by the same B cell.

Monoclonal antibodies can be used to treat diseases such as cancer. They can also be used to diagnose diseases or conditions, such as HIV.

Monoclonal antibodies can bind directly to specific cancerous cells. Once bound, they can either act directly by blocking chemical signals that promote cancerous growth or deliver targeted medication attached to the antibodies.

Monoclonal antibodies are used in the ELISA test, which can diagnose a range of diseases, including HIV.

Agglutination, marking and toxin neutralisation. 

Monoclonal antibodies are a specific, single type of antibody, where all antibodies are identical to one another.

Monoclonal antibodies are synthesized by one type of B cell in response to stimulation of B cells by helper T cells.

Monoclonal antibodies for medical use can be manufactured using mice. In this method, mice are exposed to some non-self material, which causes their B cells to produce antibodies. These B cells are then fused with cancer cells so they divide rapidly, forming hybridoma cells, from which antibodies can be extracted.

A hybridoma cell is a hybrid cell used for antibody production. It is made by fusing antibody-producing lymphocytes with human cancer cells.

Hybridoma techniques can produce many antibodies because of the use of cancer cells, which divide rapidly. This means very large quantities of antibodies can be produced for use in research and medicine.

Direct monoclonal antibody therapy is the practice of giving patients monoclonal antibodies that are complementary to antigens on cancer cells. The monoclonal antibodies bind to these antigens, blocking the chemical signals which stimulate their uncontrolled growth.

Indirect monoclonal antibody therapy involves attaching radioactive or cytotoxic drugs to monoclonal antibodies specific to cancer cells. When introduced into the patient's bodies, the monoclonal antibodies attach to cancer cells and kill them.

Antibodies on the testing strip of pregnancy tests bind to the hormone human chorionic gonadotropin (hCG), which is produced by the placenta during pregnancy. These antibodies are attached to a colored particle. Once bound, the hCG-antibody-color complex moves up the testing strip and is trapped by another antibody, forming a colored line that indicates a positive test.

The advantage of indirect monoclonal antibody therapy is that it is specific, so only a small dose needs to be used, which makes treatments relatively cheap. The disadvantage is that indirect monoclonal antibody therapy uses radioactive and cytotoxic drugs, which may cause unpleasant side effects in patients.

The advantages of direct monoclonal antibody therapy are that it does not use toxic drugs and so is unlikely to cause side effects, that it is specific so only a small dose needs to be used, and that it is relatively cheap as a treatment.

Informed consent involves making patients aware of the full risks and benefits of their treatment options before giving their consent to any medical procedures.

Monoclonal antibodies can cause severe side effects in some patients, for example in the treatment of multiple sclerosis. Patients should always be fully informed of the risks of using monoclonal antibodies before consenting to treatment.

Hybridoma techniques use mice to manufacture antibodies. Mice cannot give consent to treatment and may experience pain in the process of manufacture, such as during surgeries.

The immune system keeps the body safe using cells, organs, and proteins.

Bacteria.

Bodily fluids.

The bone marrow makes red and white blood cells and platelets.

Create T cells.

It uses memory cells and antibodies to destroy pathogens.

Red blood cell