Immune System

What is innate immunity?

Nonspecific defense that responds rapidly to pathogens

What is adaptive immunity?

Specific defense that recognizes particular antigens and develops immunological memory

Which type of immunity relies on B and T lymphocytes to recognize and destroy one specific, unique antigen fragment?

Adaptive immunity

What is the first line of defense against pathogens?

Skin and mucous membranes

How does intact skin protect against infection?

It forms a physical barrier that prevents pathogen entry

How does mucus protect mucous membranes?

It traps pathogens and particles

What do respiratory cilia do?

Move mucus and trapped pathogens toward the pharynx

What is the function of lysozyme?

Breaks down bacterial cell walls

How does stomach acid protect against pathogens?

Its low pH destroys or inhibits many microorganisms

How do normal microbiota protect the body?

Compete with pathogens for nutrients and attachment sites

What is phagocytosis?

The process of engulfing and digesting pathogens or particles

What is the first step of phagocytosis?

Chemotaxis toward a site of infection or tissue damage guided by a chemical concentration gradient

What happens during adherence in phagocytosis?

The phagocyte attaches to the pathogen

What happens during ingestion in phagocytosis?

The phagocyte engulfs the pathogen into a vesicle

What is a phagosome?

A vesicle containing an engulfed pathogen

What is a phagolysosome?

A compartment where a phagosome fuses with a lysosome for digestion

Which cells are major phagocytes?

Neutrophils, macrophages, and dendritic cells

Which phagocytes often arrive first during acute bacterial infection?

Neutrophils

What is the function of macrophages?

Engulf pathogens and debris and present antigens to T cells

What is the function of dendritic cells?

Capture antigens and activate naive T cells

What are natural killer cells?

Innate lymphocytes that patrol the body and kill virus-infected and abnormal cells that don’t have MHC proteins

How do natural killer cells kill target cells?

Release perforin and granzymes to induce cell death

What is the complement system?

A group of blood proteins that help eliminate pathogens through a cascade

What are the three major effects of complement activation?

Opsonization(tagging), inflammation, and membrane attack complex formation(lyse the target)

What is complement-mediated opsonization?

Coating pathogens with proteins such as C3b to promote phagocytosis

What is the membrane attack complex?

A complement complex that forms pores in susceptible pathogen membranes, makes them swell with water and burst(lyse).

How does complement system promote inflammation?

Complement fragments recruit immune cells and increase inflammatory responses

What are interferons?

Signaling proteins that help limit viral replication and activate immune defenses of nearby healthy cells. They act as an early warning system.

What is inflammation?

A protective response to tissue injury or infection that recruits immune defenses

What can initiate inflammation?

Tissue injury, pathogens, or recognition of harmful substances

Which cells commonly initiate inflammation?

Resident macrophages engulf debris, mast cells release histamine, and dendritic cells release cytokines.

What are cytokines?

Signaling proteins that coordinate immune and inflammatory responses

What is the role of histamine in inflammation?

Causes vasodilation and increases blood vessel permeability

What is vasodilation?

Widening of blood vessels that increases blood flow

What is increased vascular permeability?

Increased leakage of fluid and proteins from blood vessels into tissues

What causes redness during inflammation?

Increased blood flow due to vasodilation

What causes warmth during inflammation?

Increased blood flow to the affected area

What causes swelling during inflammation?

Fluid accumulation in tissues due to increased vascular permeability

What causes pain during inflammation?

Inflammatory chemicals stimulate nerves and swelling increases tissue pressure

What are the four cardinal signs of inflammation?

Redness, warmth, swelling, and pain

Why is inflammation beneficial?

Recruits immune defenses, removes damaged tissue, and promotes repair

What is fever?

A regulated increase in body temperature caused by a raised hypothalamic set point

What are pyrogens?

Substances that trigger mechanisms that raise the hypothalamic temperature set point

What are exogenous pyrogens?

Fever-inducing substances originating outside the body, such as microbial components

What are endogenous pyrogens?

Host cytokines, such as IL-1 and IL-6, that promote fever

How do pyrogens cause fever?

Stimulate prostaglandin E2 production, raising the hypothalamic temperature set point

Why can moderate fever be beneficial?

It may inhibit some pathogens and enhance immune responses

What is immunocompetence?

The ability of a lymphocyte to recognize and respond to a particular antigen

What is self-tolerance?

The ability of the immune system to avoid attacking normal body tissues

What is a naive lymphocyte?

A mature, immunocompetent lymphocyte that has not encountered its specific antigen

What is an activated lymphocyte?

A lymphocyte that has recognized its antigen and received the signals needed to respond

Where do B cells originate and mature?

They originate and mature in the bone marrow

Where do T cells originate and mature?

They originate in bone marrow and mature in the thymus

Where are naive lymphocytes commonly found?

Lymph nodes, spleen, and mucosa-associated lymphoid tissues

What is the function of cytotoxic T cells?

Kill infected, cancerous, or abnormal cells

What is the function of B cells?

Recognize specific antigens and differentiate into plasma cells and memory B cells

What are plasma cells?

Differentiated B cells that secrete antibodies

What are memory B cells?

Long-lived B cells that respond rapidly to a previously encountered antigen

What are memory T cells?

Long-lived T cells that respond more rapidly to a previously encountered antigen

What is an antigen?

A substance specifically recognized by antibodies or lymphocyte receptors that can provoke an immune response

What is an antigen receptor?

A receptor on a B or T lymphocyte that specifically recognizes an antigen or antigen-derived structure

What is an antigenic determinant or epitope?

The specific portion of an antigen recognized by an antibody or lymphocyte receptor

What is the major histocompatibility complex (MHC)?

A group of genes encoding proteins that display peptide antigens for T-cell recognition

Where are MHC class I molecules found?

On nearly all nucleated cells

What type of antigens does MHC class I present?

Primarily intracellular peptides, including viral protein fragments

Which T cells recognize MHC class I?

CD8-positive cytotoxic T cells

What is the main function of MHC class I?

Display intracellular peptide antigens for CD8 T-cell recognition

Where are MHC class II molecules found?

Primarily on dendritic cells, macrophages, and B cells

What type of antigens does MHC class II present?

Primarily peptides derived from extracellular antigens

Which T cells recognize MHC class II?

CD4-positive helper T cells

What is the main function of MHC class II?

Display extracellular antigen-derived peptides for CD4 T-cell recognition

What is an antigen-presenting cell (APC)?

A cell that processes antigens and displays peptide fragments on MHC molecules

Which cells are professional antigen-presenting cells?

Dendritic cells, macrophages, and B cells

Which cells are especially important for activating naive T cells?

Dendritic cells

How do B cells and macrophages present antigens?

Display processed pathogen peptides on MHC class II molecules

What is humoral immunity?

Adaptive immunity mediated by B cells and antibodies in body fluids

What is cell-mediated immunity?

Adaptive immunity primarily mediated by T cells acting against infected or abnormal cells

Which immune response relies mainly on antibodies?

Humoral immunity

Which immune response is especially important against virus-infected cells?

Cell-mediated immunity

What happens when a B cell is activated?

It proliferates and differentiates into plasma cells and memory B cells

What is clonal selection?

Activation of lymphocytes whose receptors specifically recognize an antigen

What is clonal expansion?

Rapid multiplication of an activated antigen-specific lymphocyte

What is an antibody?

An immunoglobulin protein produced by plasma cells that binds a specific antigen

What is the basic structure of an antibody?

Two heavy chains and two light chains joined in a Y-shaped molecule

What is antibody neutralization?

Antibodies block toxins or pathogens from binding to or entering host cells

What is antibody opsonization?

Antibodies coat pathogens and promote their ingestion by phagocytes

What is antibody agglutination?

Antibodies cross-link cells or particles, causing them to clump

What is antibody precipitation?

Antibodies bind soluble antigens and form complexes that can be cleared

How can antibodies promote inflammation?

Antigen-antibody complexes can activate the classical pathway of complement cascade

What are the five classes of antibodies?

IgG, IgA, IgM, IgE, and IgD

Which antibody class is most abundant in blood?

IgG

Which antibody class crosses the placenta?

IgG

Which antibody class is especially important in mucosal secretions such as saliva, tears, breast milk, and fluid in the gut and airways?

IgA

Which antibody class is commonly secreted as a dimer? (>-< shape)

IgA

Which antibody class is usually produced first in a primary immune response?

IgM

Which antibody class commonly forms a pentamer(like a snowflake) in blood?

IgM

Which antibody class is associated with allergies and parasite defense?

IgE

Which antibody class binds mast cells and basophils during allergic reactions?

IgE

Which antibody class functions as a receptor on naive B cells alongside IgM?

IgD

What is the primary immune response?

The response following the first exposure to a specific antigen