Immune system
60 flashcards covering Immune system for the MCAT Biology & Biochemistry section.
The immune system is your body's primary defense against infections and diseases, acting like a sophisticated network of cells, tissues, and organs that detect and eliminate harmful invaders such as bacteria, viruses, and parasites. It operates through two main branches: the innate immune system, which provides immediate, non-specific protection via barriers like skin and white blood cells, and the adaptive immune system, which develops targeted responses and "remembers" past threats for quicker future reactions. This system is crucial for maintaining health and is foundational in understanding diseases like allergies and autoimmune disorders.
On the MCAT, the immune system frequently appears in the Biology and Biochemistry section through multiple-choice questions that test concepts like immune cell functions, antibody production, and vaccine mechanisms. Common traps include confusing similar terms, such as T-cells versus B-cells, or overlooking how environmental factors influence immune responses. Focus on integrating knowledge of molecular processes, like antigen presentation and inflammation pathways, as questions often involve passage analysis or experimental scenarios to assess critical thinking.
Practice drawing immune response diagrams to solidify your understanding.
Terms (60)
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Innate Immunity
Innate immunity is the body's first line of defense against pathogens, involving non-specific mechanisms like physical barriers, phagocytic cells, and the complement system that respond rapidly but do not adapt over time.
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Adaptive Immunity
Adaptive immunity is a specific immune response that develops over time, involving lymphocytes such as T cells and B cells, which recognize and remember specific antigens for a targeted and enhanced response upon re-exposure.
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Antigen
An antigen is any substance, typically a foreign molecule like a protein or polysaccharide from a pathogen, that can trigger an immune response by being recognized by antibodies or T cell receptors.
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Antibody
An antibody is a Y-shaped protein produced by B cells that binds specifically to antigens, neutralizing pathogens or marking them for destruction by other immune components.
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B Lymphocyte
B lymphocytes, or B cells, are white blood cells that produce antibodies and are central to humoral immunity, maturing in the bone marrow and activating upon antigen encounter to form plasma cells.
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T Lymphocyte
T lymphocytes, or T cells, are white blood cells that orchestrate cell-mediated immunity, including helper T cells that activate other immune cells and cytotoxic T cells that kill infected cells.
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Helper T Cell
Helper T cells are a subset of T lymphocytes that release cytokines to stimulate B cells, cytotoxic T cells, and macrophages, playing a key role in coordinating the adaptive immune response.
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Cytotoxic T Cell
Cytotoxic T cells are T lymphocytes that directly kill infected or abnormal cells by recognizing antigens presented on MHC class I molecules and inducing apoptosis in the target cells.
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Memory Cell
Memory cells are long-lived lymphocytes, derived from B or T cells, that remain in the body after an infection, allowing for a faster and stronger immune response upon subsequent exposure to the same antigen.
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Phagocytosis
Phagocytosis is the process by which certain immune cells, like macrophages and neutrophils, engulf and destroy pathogens or debris, serving as a key mechanism in innate immunity.
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Macrophage
Macrophages are large phagocytic cells derived from monocytes that engulf pathogens, present antigens to T cells, and release inflammatory signals to enhance immune responses.
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Neutrophil
Neutrophils are the most abundant white blood cells and are primary responders in innate immunity, using phagocytosis and releasing enzymes to combat bacterial infections.
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Dendritic Cell
Dendritic cells are antigen-presenting cells that capture pathogens, process them, and present antigens to T cells in lymph nodes, bridging innate and adaptive immunity.
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Natural Killer Cell
Natural killer cells are lymphocytes that detect and destroy virus-infected cells or tumor cells by releasing cytotoxic substances, without requiring prior sensitization.
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Complement System
The complement system is a group of proteins in the blood that enhances antibody and phagocytic responses by opsonizing pathogens, promoting inflammation, and directly lysing certain bacteria.
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Inflammation
Inflammation is a localized immune response to injury or infection, characterized by redness, heat, swelling, and pain, mediated by chemicals like histamines and cytokines to isolate and eliminate threats.
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Cytokines
Cytokines are small signaling proteins released by immune cells that regulate inflammation, cell growth, and immune responses, such as interleukins that facilitate communication between cells.
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Interferons
Interferons are a type of cytokine produced by virus-infected cells that inhibit viral replication and activate immune cells, playing a crucial role in antiviral defense.
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Histamine
Histamine is a chemical released by mast cells and basophils during allergic reactions or tissue injury, causing vasodilation and increased permeability to recruit immune cells to the site.
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Humoral Immunity
Humoral immunity involves antibodies in bodily fluids that neutralize extracellular pathogens, primarily mediated by B cells and their plasma cell derivatives.
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Cell-Mediated Immunity
Cell-mediated immunity targets intracellular pathogens and abnormal cells using T cells, such as cytotoxic T cells, rather than antibodies.
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Clonal Selection
Clonal selection is the process where a specific lymphocyte clone is activated and proliferates in response to its matching antigen, leading to an effective immune response.
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Primary Immune Response
The primary immune response is the initial reaction to an antigen, which is slower and less intense, involving the activation of naive lymphocytes.
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Secondary Immune Response
The secondary immune response is a rapid and stronger reaction to a previously encountered antigen, due to the presence of memory cells.
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Active Immunity
Active immunity develops after exposure to an antigen, either through infection or vaccination, where the body produces its own antibodies and memory cells.
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Passive Immunity
Passive immunity is acquired through the transfer of antibodies from another source, such as from mother to child, providing immediate but temporary protection.
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Vaccination
Vaccination introduces a harmless form of an antigen to stimulate active immunity, training the immune system to recognize and fight the actual pathogen upon future exposure.
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Autoimmune Disease
Autoimmune diseases occur when the immune system mistakenly attacks the body's own tissues, such as in rheumatoid arthritis, due to a breakdown in self-tolerance.
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Hypersensitivity
Hypersensitivity refers to an exaggerated immune response to an antigen, categorized into types like immediate allergic reactions or delayed responses that can cause tissue damage.
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HIV
HIV is a virus that attacks CD4+ helper T cells, leading to acquired immunodeficiency syndrome (AIDS) by weakening the immune system's ability to fight infections.
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Major Histocompatibility Complex
The major histocompatibility complex (MHC) is a set of cell surface proteins that present antigens to T cells, with MHC class I on most cells and MHC class II on antigen-presenting cells.
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Antigen Presentation
Antigen presentation is the process where cells display antigen fragments on MHC molecules to T cells, initiating an adaptive immune response.
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Opsonization
Opsonization is the coating of pathogens with antibodies or complement proteins, enhancing their recognition and phagocytosis by immune cells.
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Apoptosis
Apoptosis is programmed cell death induced by cytotoxic T cells or other signals, helping to eliminate infected or damaged cells without causing inflammation.
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Fever
Fever is an elevated body temperature response orchestrated by the immune system, often triggered by pyrogens, which inhibits pathogen growth and enhances immune function.
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Lymph Nodes
Lymph nodes are small structures where lymphocytes congregate to encounter antigens, facilitating the activation and proliferation of immune cells.
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Spleen
The spleen is an organ that filters blood, removes old red blood cells, and serves as a site for immune responses, including the activation of B and T cells.
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Thymus
The thymus is a gland where T lymphocytes mature and undergo selection to ensure they can distinguish self from non-self antigens.
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Bone Marrow
Bone marrow is the site of hematopoiesis, producing all blood cells including lymphocytes, and is crucial for the development of B cells.
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Immunoglobulin G
Immunoglobulin G (IgG) is the most abundant antibody in serum, providing long-term immunity by crossing the placenta and neutralizing pathogens.
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Epitope
An epitope is the specific region on an antigen that is recognized by an antibody or T cell receptor, determining the antigen's immunogenicity.
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Pathogen
A pathogen is any microorganism, such as a virus or bacterium, that can cause disease by evading or overwhelming the immune system.
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Herd Immunity
Herd immunity occurs when a significant portion of a population is immune to a pathogen, reducing its spread and protecting vulnerable individuals.
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Immune Tolerance
Immune tolerance is the state where the immune system does not respond to self-antigens, maintained through mechanisms like clonal deletion in the thymus.
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Cross-Reactivity
Cross-reactivity happens when an antibody or T cell recognizes similar epitopes on different antigens, potentially leading to immune responses against unintended targets.
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Immunosuppression
Immunosuppression is a reduction in immune function, often due to drugs or diseases like HIV, increasing susceptibility to infections.
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Allergy
An allergy is a type I hypersensitivity reaction where the immune system overreacts to harmless antigens, like pollen, triggering symptoms such as sneezing.
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Anaphylaxis
Anaphylaxis is a severe, life-threatening allergic reaction involving widespread histamine release, causing symptoms like swelling, low blood pressure, and difficulty breathing.
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MHC Class I vs. MHC Class II
MHC class I presents endogenous antigens to cytotoxic T cells on most nucleated cells, while MHC class II presents exogenous antigens to helper T cells on antigen-presenting cells.
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Toll-Like Receptors
Toll-like receptors are pattern recognition receptors on immune cells that detect pathogen-associated molecular patterns, initiating innate immune responses.
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Cytokine Storm
A cytokine storm is an overwhelming release of cytokines that causes excessive inflammation and tissue damage, often seen in severe infections or autoimmune conditions.
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Autoimmunity Mechanism
Autoimmunity mechanisms include molecular mimicry, where pathogens resemble self-antigens, leading the immune system to attack host tissues.
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Strategy for Distinguishing Innate and Adaptive Immunity
To distinguish innate and adaptive immunity, note that innate responses are immediate and non-specific, while adaptive responses are delayed, specific, and involve memory.
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Common Trap: Confusing B and T Cell Functions
A common error is confusing B cells, which produce antibodies for humoral immunity, with T cells, which handle cell-mediated immunity and direct killing.
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Worked Example: How a Vaccine Works
In a vaccine example, an inactivated virus is introduced, activating B cells to produce antibodies and T cells for memory, so the body can quickly respond to the real virus later.
For the flu vaccine, a killed virus strain prompts immunity without causing illness.
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Clonal Expansion
Clonal expansion is the rapid proliferation of antigen-specific lymphocytes after activation, amplifying the immune response to effectively clear the pathogen.
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Interferon Types
Interferons include type I (like alpha and beta) for antiviral effects and type II (gamma) for activating macrophages, each targeting specific immune functions.
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Opsonin
An opsonin is a molecule, such as an antibody or complement protein, that binds to pathogens to facilitate their phagocytosis by immune cells.
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Lymphocyte Activation
Lymphocyte activation requires two signals: antigen binding to the receptor and co-stimulatory signals from other cells, ensuring a controlled immune response.
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Immune Evasion by Pathogens
Pathogens evade the immune system by altering antigens, hiding in host cells, or suppressing immune responses, as seen in viruses like HIV.