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Immune Response

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Immune Response

The immune response is how an organism responds after being infected with a pathogen. A pathogen can be bacteria, viruses, or toxins. The immune response consists of both innate and adaptive immune responses.

On pathogens, proteins live on the surface, known as antigens. There are specific antigens for each type of pathogen. Lymphocytes, a variety of white blood cells, can differentiate between whether or not a cell is an antigen or a cell from the body. Once they can differentiate, they produce antibodies to help destroy the antigens.

What does the innate immune response do?

The innate immune response, aka non-specific immune response, defends the body against non-specific pathogens and is considered the first line of defence. Parts of the body such as skin and mucus form the innate immune response by keeping out pathogens. The mucus in our nose traps the pathogens from getting inside our bodies, and they also use their form of bacteria to destroy the stuck pathogens. In addition, various other cells are involved in the innate immune response as they carry out 'cell eating' – phagocytosis. These additional cells include neutrophils, macrophages, and monocytes.

What do the cells in the innate immune response do?

The cells in the innate immune response are white blood cells that include neutrophils, macrophages, and monocytes.

  • Neutrophils are the most abundant type of white blood cell and are the first to fight back against a pathogen. They can do this by releasing enzymes that digest and kill pathogens.
  • Macrophages are another type of white blood cell made in the bone marrow. These macrophages play a role in inflammation by releasing cytokines small proteins that help with inflammation and act as messengers between other cells.
  • Monocytes are another type of white blood cell and can turn into macrophages. They also play a role in the adaptive immune system.

Despite their many differences, they are all able to perform phagocytosis

What does the adaptive immune response do?

While the innate immune system remains the same from birth, the adaptive immune system can learn over time. The adaptive immune response works to fight off pathogens and is especially effective against those it has destroyed before. Each time it encounters a pathogen, it will remember it in its memory, and it will be faster to defeat each time it sees it.

An example of an adaptive immune response is chickenpox. If someone gets sick with chickenpox regardless of age, they will never contract it again after fighting it off the first time.

There are only two types of cells in the adaptive immune response, T and B cells. T and B cells come from stem cells located in the bone marrow, and they are both classified as lymphocytes, which means they are the primary type of cell found in the lymph.

Figure 1

Although it is effective, it is slower to respond than the innate immune response due to it needing to identify the antigen before responding. This immune response splits into two types – humoral and cellular immunity. The adaptive immune response also requires fewer cells than the innate immune response.

What is humoral immunity?

Humoral immunity, or antibody-mediated immunity, is mediated by B cells. B cells move through the lymphatic system, where they encounter an antigen. Suppose the antigen matches the specific antibody on their cell surface, a membrane-bound antibody. In that case, they either split into a memory B cell, or an effector B cell occurs when plasma cells produce antibodies and allow them to move throughout the body.

Humoral immunity splits into both primary and secondary immune responses.

What are primary and secondary immune responses?

Primary immune responses occur when the body encounters a pathogen for the first time. These immune responses use the naive B and T cells. As the B and T cells have not transformed into their effector and memory cells, they are slow to respond to the threat to the point where it takes several days to react.

In contrast, the secondary immune response uses the memory forms of the B and T cells. Therefore, they respond in about half the time the primary response takes. They also produce higher levels of antibodies compared to the primary immune response.

This quicker response is why someone can never be infected with chickenpox again for the rest of their life.

Have you noticed that your armpits are sometimes swollen when you are ill? This is because your armpits are rich in lymph nodes, which contain lymphocytes. Swelling of the lymph nodes indicates high lymphocyte activity.

What is cellular immunity?

Cellular immunity involves the activation of lymphocytes upon encountering a 'non-self' material and is mediated by T cells. T cells are created in the bone marrow but travel to the thymus, a small organ located in the chest to get transformed into T cells. In the thymus, they develop T cell receptors where they will get a T cell receptor named CD4 or CD8. The different receptors allow the cells to perform different tasks.

Therefore, there are three types of T cells. Their jobs depend on what T cell receptor they receive. The Helper T cells have CD4 and help B cells and other cells found in the immune response. Cytotoxic T cells have CD8 and destroy pathogens plus infected self cells.

T regulatory cells have both CD4 and CD25, and its job is to identify what cells belong to the body, so they will not be attacked.

The receptors also need to perform recombination of genes that express these receptors. It is called rearrangement, and it allows for a large amount of diversity in the genes. Still, occasionally a mistake happens, and the gene is rearranged into an identical gene found in a person. This mistake leads to the body attacking itself. To prevent this response, T cells are tested twice by the body. The first test is to make sure they can tell the difference between their body's proteins and the proteins of a pathogen. The second test is to see how it will bind. If it attaches to something that is not an antigen or itself, it will be eliminated.

How do vaccines help the immune response?

Vaccines help the immune response by pretending to be a pathogen. This makes the immune system believe that it is sick and needs to produce antibodies. Now that the immune system remembers how to fight off this pathogen, it can fight it off faster if the body ever actually becomes infected. The figure below shows a quick diagram of how it works.

Figure 2

Immune Response - Key takeaways

  • The immune response is how an organism responds after being infected with a pathogen aka a form of bacteria, virus, or toxin.

  • Pathogens have proteins on their surface called antigens.

  • Antibodies are produced by the body and used to destroy pathogens.

  • There are innate and adaptive immune responses. Innate responses are nonspecific and what an organism was born with. Adaptive responses can grow as the organism comes in contact with pathogens and has two types of immunity, humoral and cellular.

  • Humoral immunity consists of B cells that either produce antibodies or remember previous pathogen attacks. Cellular immunity is when cells not belonging to the body are identified and are then destroyed by T cells.

Frequently Asked Questions about Immune Response

During an immune response, cells in the innate immune system notice a pathogen. Cytokines are then released, the complement system is activated, and then the innate immune system calls for inflammatory responses.

The types of immune systems are innate, adaptive, primary, and secondary immune responses.

Producing antibodies and remembering prior pathogens

The immunity is through cells and not antibodies. Also, the cells are able to cooperate to help take down the pathogens.

Final Immune Response Quiz

Question

What type of molecule is an antibody?

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

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How are antibodies produced?

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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.

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What is the structure of an antibody?


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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.

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Where is the antigen-binding site on an antibody?


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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.

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Why are the variable and constant regions named as they are?


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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.

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What is agglutination?


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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.

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How do antibodies neutralise toxins?


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

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What is the antigen-antibody complex?


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

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How do antibodies stimulate phagocytosis?


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

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How does the structure of an antibody make agglutination possible?


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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.

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What are monoclonal antibodies?


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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.

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What are the uses of monoclonal antibodies?


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

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How can monoclonal antibodies be used to treat cancer?


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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.

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How can monoclonal antibodies be used for diagnosing diseases?


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

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What are the 3 main functions of antibodies?

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Agglutination, marking and toxin neutralisation. 

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What is the definition of a monoclonal antibody?

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

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How are monoclonal antibodies produced in the immune response?

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

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How can monoclonal antibodies be produced for clinical use?


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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.

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What is a hybridoma cell?


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

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What is the advantage of using hybridoma techniques to manufacture antibodies?


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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.

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What is direct monoclonal antibody therapy?


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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.

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What is indirect monoclonal antibody therapy?


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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.

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How are antibodies used in pregnancy tests?


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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.

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What are the advantages and disadvantages of indirect monoclonal antibody therapy?


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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.

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What are the advantages of direct monoclonal antibody therapy?


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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.

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What is informed consent?


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

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What are the ethical issues with the use of monoclonal antibodies on patients?


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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.

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What is the disadvantage of using hybridoma techniques to manufacture antibodies?


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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.

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What is an immune response?

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An immune response is how an organism responds after being infected by a pathogen.

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The two types of immune responses include innate and active immune responses.

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True

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What cells does the innate immune response have?

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B and T cells

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What does the complement system do in the immune response?

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It uses antibodies to destroy pathogens and creates inflammation.

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What type of cell makes up most of the innate immune response cells?


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Red blood cells.

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Where are most of these immune response cells made?


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The bone marrow.

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What are the two types of adaptive immune responses?


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Humoral and cellular immunity.

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What is the difference between effector and memory B cells?


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Memory cells are longer lived than the effector cells.

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What do T cells do?


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Destroy pathogens.

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What does the innate immune response use as a defence against pathogens?


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 Skin, mucus, and various cells.

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What are the T cell receptors?


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CD4, CD8, and CD25.

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Which response has a higher amount of antibodies: primary or secondary?


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Secondary response.

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What type of cells do primary immune responses use?


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Memory B and T cells.

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What does pinocytosis do?

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It consumes liquids.

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What is phagocytosis?

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A process in which cells attach themselves to pathogens to destroy them.

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What are the steps of phagocytosis?

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Activation, Chemotaxis, Attachment, Consumption, Exocytosis

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What is exocytosis?


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It is a process that allows cells to remove waste from their inside.

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Phagocytes need to be in physical contact with whatever they want to devour.


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True

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Can unicellular organisms also perform phagocytosis?


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No

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What do osteoclasts do?


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Destroy bone by dissolving it.

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Can more of these phagocytosis cells be made?


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Yes.

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 Why do unicellular organisms do phagocytosis?


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They do it to eat.

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