Immune System
Unit 16 Synopsis
The immune system functions of recognize, fight, and defend against foreign substances at a cellular level.
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Self
Anti-
Against
Cyto-
cell
Phago-
Eat
Xeno-
Foreign
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to stand
Hetero-
Different
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Same
Key Terms
Immunity: resistance to disease
Pathogen: a microorganism, such as bacteria or viruses that can cause disease
Antigen: Anything that causes an immune response
Antibody: immune system proteins that bind to antigens
Herd Immunity: enough people are vaccinated so the microbes cannot spread
Overview
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Function = Recognize, fight, and defend against foreign substances at a cellular level
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Relies heavily on WBCs (specifically lymphocytes) in lymphoid tissues and organs
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Goal is to achieve immunity
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Antigen
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Ex. Bacterium, fungus, or virus, but could also be a toxin or diseased/cancerous cell in your own body
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They act as signaling molecules to induce an immune response in the body (such as the production of antibodies)
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Note: antigens aren't always toxins, pathogens, or cancer cells
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Your red blood cells have proteins on their plasma membranes that are antigens, and your body can only tolerate blood that has the same antigens as your blood cells. For example, Type A blood type means those people have A antigens on their red blood cells. This means if you take in Type A blood, your body recognizes it and receives it. If you were to take in Type B blood which has Type B antigens, your body would reject it because it has developed antibodies that are anti-B antigens, since those are considered foreign substances. People with Type AB blood have both A and B antigens present. Type O blood has no antigens which is why people of any blood type can accept it. ​
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Non-Specific Immunity (Innate)
Rapid response time
On guard at all times, ready to attack anything and everything, but without specificity.
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First Line of Defense
Skin acts as a mechanical barrier
Mucous membranes line all body cavities that open to the exterior, in the respiratory, digestive, urinary, and reproductive tracts
contains protective chemicals
acid secretions, enzymes, and defensins (antimicrobial proteins)
Other protective features include nasal hairs, cilia, and mucus
Second Line of Defense (internal)
Antimicrobial proteins attack microorganisms directly and/or make it hard for them to reproduce
Interferons: small signaling proteins secreted by virus-infected cells that diffuse to nearby uninfected cells to block viral takeover; get the immune system mobilized
Complement proteins - enhance antibody function; ​plasma proteins that, when activated, causes an amplified inflammatory response. These can also be secreted by lymphocytes.
Can also lyse microorganisms
Natural Killer Cells - induce apoptosis
*Help with killing both cancerous cells and virus-infected cells
*Use the protein perforin to create pores in the cell membrane of the infected cell and inject enzymes (like granzymes) that will stimulate the cell to do apoptosis
*They are called “natural” killer cells because of their lack of specificity – they just see anything that is not “self” or “natural”, and they kill it
*This attack strategy is the same one that cytotoxic T cells
Phagocytosis
Chemotaxis -> opsonization -> adherence -> ingestion -> killing
More detailed explanation:
1. Activation of Phagocytic Cells: The process begins with the activation of phagocytic cells, such as macrophages or neutrophils. These cells are activated by signals from their environment, which could be chemicals released by pathogens or damaged cells
2. Chemotaxis: Following activation, the phagocytes move towards the site of infection or damage through a process known as chemotaxis. They are guided by a concentration gradient of chemotactic factors
3. Recognition and Attachment: The phagocyte recognizes the pathogen through specific receptors on its surface. These receptors can bind to molecules on the pathogen’s surface. Once bound, the phagocyte begins to extend its membrane around the pathogen
4. Ingestion: The phagocyte’s membrane envelops the pathogen, forming pseudopodia around it. This eventually leads to the engulfment of the pathogen within a vesicle known as a phagosome
5. Formation of Phagolysosome: The phagosome then fuses with a lysosome, which is an organelle containing digestive enzymes. The fusion creates a phagolysosome, where the pathogen is exposed to a hostile environment and destructive enzymes
6. Digestion: Inside the phagolysosome, the pathogen is broken down by lysosomal enzymes into smaller components that can be used by the cell or disposed of
7. Exocytosis: The final step involves the elimination of the digested material from the phagocyte. The residual bodies containing indigestible material are moved to the cell surface and expelled through exocytosis
Performed by phagocytes that eat pathogens
e.g. neutrophils: the most abundant leukocyte that releases pus; macrophages are "big eaters" that use cytoplasmic extensions to reel in and "eat" foreign invaders
Some pathogens (like the bacteria that causes tuberculosis) are resistant to the lysosomal enzymes, and thus helper T cells (another type of immune cell discussed later in the notes) release chemicals to stimulate the macrophages, activating additional enzymes to come in and kill the pathogens.
Inflammation
Nonspecific response to tissue injury that leads to an internal chemical alarm
Pain, swelling, redness, heat
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Preventing the damaging invaders from spreading to nearby tissues
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Getting rid of cell debris and pathogens
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Alerting our adaptive defense
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Getting injured area ready to be repaired
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Phagocytes are mobilized
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Injured/stressed tissue cells and immune cells release inflammatory chemicals, like:
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Histamine: promotes arteriole vasodilation 🡪 increased blood flow to injury
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Released by basophils and mast cells (two types of WBCs)
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Kinins and Prostaglandins: promote arteriole vasodilation AND induce pain
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Complement proteins: amplify the response
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Cytokines: chemical messenger proteins of the immune system that aid in coordinating it all
Vasodilation --> Phagocytic emigration --> tissue repair
Fever
abnormally high body temperature
a systemic response to invaders
pyrogens: released by immune cells which raise the body's temperature
inhibits pathogens from multiplying
increases the metabolic rate of tissue cells to speed up the repair process
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Specific Immunity (Adaptative)
Depends on the cell's ability to recognize/remember and bind antigens, and communicate with each other to initiate a specific response
The adaptive immune system is systemic, meaning it isn’t restricted to the initial infection site like in innate defense
Babies are not born with adaptive immunity, and it takes time to develop. Babies that are breastfed receive antibodies from the mother’s breastmilk, but they still have to develop their own immune system for after they are no longer breastfed.
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Depends on the ability of cells to:
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Recognize/remember antigens (must be introduced to a specific pathogen and identify it as a threat)
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Bind to them, and
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Communicate with each other to initiate a specific response
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​The adaptive defense system is a much more elite fighting force but is only equipped to attack substances that have been identified by the body as foreign.
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Antigens
Self-recognition: immunological tolerance
Cytokines
Interleukins
Interferons
Perforin
Cell-mediated (Cellular)
T lymphocytes cells: leukocytes that are made in the red bone marrow and matured in the thymus
Act as a “special forces unit” in your cells that cause inflammation, activate macrophages, and regulate the immune response
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Do not have the ability to recognize and respond to antigens like B cells so they are reliant on antigen-presenting cells (APCs)
APCs: engulf antigens and present fragments on their surfaces for the T cells to recognize and respond to
Includes: dendritic cells, macrophages, B cells
Cytotoxic
Directly attack and kill other cells (via apoptosis)​
Cytotoxic T cells, also known as CD8+ T cells, play a crucial role in the immune system by identifying and destroying infected or cancerous cells in the body. They do this by recognizing antigens on the surface of these abnormal cells and releasing toxic substances that cause the cells to die. This process helps to prevent the spread of disease and maintain overall health.
Helper
help activate B, T cells, and macrophages
Helper T cells, also known as CD4 T cells, play a crucial role in the immune system by recognizing and responding to foreign antigens. They help activate and coordinate other immune cells, such as B cells and cytotoxic T cells, to fight off infections and diseases.​
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Memory
Remember the antigen and moderate the immune system
​Memory T cells are a type of immune cell that are responsible for remembering past infections and helping the body to fight off future infections. They are able to quickly recognize and respond to pathogens that they have encountered before, which helps to provide long-lasting immunity against certain diseases.
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Antigen-Presenting Cells
Cells that engulf antigens and then present their fragments on their surfaces so that T cells can recognize them and respond to them
*Dendritic cells in the skin use their extensions to “catch” antigens and take them to T cells in a lymph node
*Macrophages distributed throughout the lymphoid organs and connective tissue can phagocytize the antigens or activate T cells to do so
*B cells present antigens to helper T cells, which in turn activate them
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T-Cell Activation
APC presents antigen in fragments
T cell recognizes it and binds
Activates the T cell
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Antibody-Mediated (Humoral)
B cells
Leukocytes made and matured in bone marrow
Differentiate into plasma cells that will secrete antibodies that can either:
Inactivate the antigens through:
neutralizations: a way of using the antibodies to mask the dangerous parts of viruses and the toxins that bacteria secrete so they can’t bind on receptor and the phagocytes can eventually destroy them
agglutination: antibodies bind to cells and clump them together so they are all in one place to be phagocytized
precipitation: soluble molecules use antibodies to gather up antigens into a ”precipitated antigen molecule” that the phagocytes can more easily capture and engulf
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Mark antigens for destructions to activate complement proteins that enhances the inflammation and leads to cell lysis
Some B cells will become memory cells
Allows the body to remember and respond more quickly if they encounter the antigen again in the future 🡪 immunological memory
Immunoglobulins
Complement System
Vaccines
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Vaccination: substances used to stimulate your immune system to guard against attack
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Used to prevent viral and bacterial diseases
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Expose immune system to antigens before infection
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Trick immune system to make antibodies that your body will remember how to make if the real thing invades later to decrease response time
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Vaccinations are made from a weakened virus, inactivated virus, or part of a virus/bacteria
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These stimulate the immune system to react, preparing the body for future invasions
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Vaccines work because of herd immunity
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When enough people are vaccinated, the microbes aren’t able to spread
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. One of the common misunderstandings is that vaccines can cause autism. However, this has been thoroughly debunked by numerous studies and medical professionals. It's important rely on accurate information and consult with a healthcare provider to make informed decisions about vaccinations.
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