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Innate immunity

Nonspecific defenses that act immediately and do not produce memory; includes physical barriers, phagocytes, inflammation, fever, complement, and interferons.

Adaptive immunity

Specific defenses that develop over time, involve B and T cells, and produce memory cells.

Physical barriers (innate immunity)

Skin, mucous membranes, cilia, and normal microbiota that block pathogen entry.

Internal innate defenses

Phagocytes, NK cells, inflammation, fever, complement system, and interferons.

Myeloid stem cells

Develop into basophils, eosinophils, neutrophils, dendritic cells, and monocytes.

Lymphoid stem cells

Develop into B lymphocytes, T lymphocytes, and Natural Killer (NK) cells.

Phagocytosis

Chemotaxis, adherence, ingestion, and digestion of pathogens by phagocytes.

Microbial resistance to phagocytosis

Capsules, inhibition of phagolysosome formation, survival inside phagosomes, or escape into cytoplasm.

Lymphatic system

Includes lymph, lymph vessels, and lymph nodes; supports innate and adaptive immunity by filtering pathogens and housing immune cells.

Benefits of fever

Inhibits microbial growth, increases metabolism, enhances immune response, and speeds tissue repair.

Histamine

Chemical released during inflammation that increases vessel permeability.

Vasodilation

Widening of blood vessels to increase blood flow to infected tissue.

Edema

Swelling caused by fluid leakage from blood vessels.

Bradykinin

Causes pain, vasodilation, and increased vascular permeability.

Diapedesis

Movement of white blood cells out of blood vessels into tissues.

Pus

Collection of dead WBCs, bacteria, and tissue debris.

Fibroblasts

Cells that produce collagen during tissue repair.

Chronic inflammation

Long-term inflammation that can lead to tissue damage and granuloma formation.

Granuloma

Mass of immune cells that walls off and limits spread of an infectious agent.

Interferon

Protein released by virus-infected cells that induces antiviral proteins in neighboring cells.

Complement system

Cascade of plasma proteins that enhance immune responses.

Opsonization

Complement or antibody coating of pathogens to enhance phagocytosis.

Membrane attack complex (MAC)

Complement proteins that form pores in pathogen membranes causing cell lysis.

Active immunity

Immunity produced by the body’s own immune response; long-lasting with memory.

Passive immunity

Immunity acquired by receiving antibodies; short-term and no memory.

Natural active immunity

Immunity gained from natural infection.

Artificial active immunity

Immunity gained from vaccination.

Natural passive immunity

Antibodies transferred from mother to infant (placenta or breast milk).

Artificial passive immunity

Injection of pre-formed antibodies.

Antigen

Substance that triggers an immune response.

Epitope

Specific region of an antigen recognized by antibodies or receptors.

Hapten

Small molecule that becomes antigenic only when attached to a carrier protein.

Humoral immunity

Antibody-mediated immunity involving B cells.

Cell-mediated immunity

Immunity involving T cells that directly attack infected cells.

Characteristics of adaptive immunity

Self vs non-self recognition, specificity, diversity, and memory.

B cell antigen recognition

B cells use surface IgM to bind antigen.

Plasma cells

B cells that secrete large quantities of antibodies.

Antibody structure

Two heavy chains and two light chains with variable and constant regions.

Variable region of antibody

Binds specific antigen.

Constant region of antibody

Determines antibody class and immune function.

IgG

Most abundant antibody; opsonization and crosses placenta.

IgA

Found in secretions such as saliva, mucus, and breast milk.

IgM

First antibody produced; activates complement.

IgE

Involved in allergies and parasitic infections.

IgD

Found on B cell surface; regulatory role.

Primary immune response

First exposure to antigen; slow and mainly IgM production.

Secondary (anamnestic) response

Faster and stronger response due to memory cells; mainly IgG.

Class switching

Change in antibody class without changing antigen specificity.

T-cell independent antigens

Activate B cells without T helper cells.

T-cell dependent antigens

Require T helper cells for B cell activation and memory formation.

T helper cells (CD4+)

Recognize antigen on MHC II and release cytokines.

T cytotoxic cells (CD8+)

Recognize antigen on MHC I and kill infected cells via perforins and granzymes.

Natural Killer cells

Kill abnormal cells without antigen presentation.

T regulatory cells

Suppress immune responses when no longer needed.

Types of vaccines

Live attenuated, inactivated, subunit, toxoid, conjugate, and mRNA.

Live attenuated vaccines

Weakened pathogens that produce strong, long-lasting immunity.

Inactivated vaccines

Killed pathogens; safer but require boosters.

Subunit vaccines

Contain only antigenic parts of the pathogen.

Toxoid vaccines

Contain inactivated toxins.

Conjugate vaccines

Polysaccharides linked to proteins to enhance immune response.

mRNA vaccines

Provide instructions for host cells to make antigen.

Sensitivity (diagnostic tests)

Ability to correctly identify those with disease.

Specificity (diagnostic tests)

Ability to correctly identify those without disease.

Monoclonal antibodies

Identical antibodies specific to one epitope.

Hybridoma cells

Fusion of B lymphocyte and myeloma cell to produce monoclonal antibodies.

Precipitation reaction

Soluble antigen and antibody form insoluble complexes.

Agglutination

Antibodies cause clumping of particulate antigens.

Hemagglutination

Agglutination involving red blood cells.

Neutralization

Antibodies block toxins or viruses from binding to host cells.

Complement-fixation test

Antigen–antibody complex activates complement; no hemolysis indicates positive.

ELISA assay

Enzyme-linked antibodies produce color change when antigen is present.

Rapid antigen test

Detects pathogen antigens using antibodies on test strips.

Fluorescence microscopy detection

Uses fluorescent-labeled antibodies to visualize pathogens.

Type I hypersensitivity

IgE-mediated immediate reaction involving mast cell degranulation.

Type II hypersensitivity

IgG or IgM antibodies target cell surface antigens causing cell destruction.

Type III hypersensitivity

Immune complex deposition leading to inflammation.

Type IV hypersensitivity

T-cell mediated delayed response without antibodies.

Cancer immune surveillance

Immune system detects and destroys abnormal cells.

Immunotherapy

Cancer treatment that enhances immune responses.

Epidemiology

Study of disease distribution in populations.

Etiology

Cause of a disease.

Morbidity

Rate of illness in a population.

Mortality

Rate of death in a population.

Endemic

Disease constantly present in a population.

Epidemic

Sudden increase in disease cases.

Pandemic

Worldwide spread of disease.

Incidence

Number of new disease cases over time.

Prevalence

Total number of disease cases at a given time.

Zoonosis

Disease transmitted from animals to humans.

Herd immunity

Protection of population due to high immunity levels.

Contact transmission

Direct or indirect transmission between people or objects.

Vehicle transmission

Transmission via food, water, blood, or air.

Vector transmission

Transmission via insects or animals.

Fomite

Nonliving object that transmits pathogens.

Koch’s Postulates

Criteria linking a specific microorganism to a disease.

Stages of disease

Incubation, prodromal, illness, decline, and convalescence.

Nosocomial infection

Healthcare-associated infection.

Universal Precautions

Practices to reduce infection spread in healthcare settings.

Emerging infectious diseases

Diseases increasing due to environmental, social, or biological factors.

Descriptive epidemiological studies

Describe disease patterns.