Immunology: Innate and Adaptive Defense Mechanisms, Cells, and Vaccines

First line of defense

Physical and biochemical barriers preventing infection (skin, mucous membranes, secretions)

Second line of defense

Innate/nonspecific immunity that is fast, broad, and has no memory

Third line of defense

Adaptive/specific immunity with memory and pathogen specificity

Normal microbiota function

Competitive exclusion, nutrient consumption, and production of antimicrobial compounds

Lysozyme function

Enzyme that breaks down bacterial cell walls found in tears and saliva

Phagocytosis

Process by which cells engulf and destroy pathogens

Neutrophils

First responders that engulf and destroy pathogens

Macrophages

Phagocytes that engulf pathogens and signal other immune cells

Dendritic cells

Antigen-presenting cells that activate adaptive immunity

Natural killer (NK) cells

Destroy infected or abnormal cells

Inflammation signs

Redness, heat, swelling, pain

Interferons

Antiviral proteins that interfere with viral replication

Complement system

Protein cascade that enhances immune response

C3b function

Opsonization (tags pathogens for phagocytosis)

C5a function

Attracts phagocytes and promotes inflammation

Membrane attack complex (MAC)

Complex that lyses pathogen cell membranes

Pattern recognition receptors (PRRs)

Receptors that recognize PAMPs on pathogens

PAMPs

Pathogen-associated molecular patterns recognized by innate immunity

Toll-like receptors

Membrane receptors that detect extracellular pathogens

NOD-like receptors

Cytoplasmic receptors that detect cell damage or infection

RIG-like receptors

Detect viral RNA and trigger interferon production

Chemotaxis

Movement of immune cells toward infection signals

Opsonization

Tagging pathogens to enhance phagocytosis

Adaptive immunity

Specific immune response with memory that develops over time

B cells

Lymphocytes that produce antibodies

T cells

Lymphocytes that recognize antigens presented on MHC molecules

Helper T cells (CD4)

Activate B cells and macrophages

Cytotoxic T cells (CD8)

Kill infected host cells via apoptosis

Antigen

Molecule that triggers an immune response

Epitope

Specific part of antigen recognized by immune cells

Clonal selection

Activation and proliferation of lymphocytes specific to an antigen

Plasma cells

B cells that produce antibodies

Memory cells

Long-lived cells that provide faster response upon re-exposure

MHC I

Presents endogenous antigens on all nucleated cells

MHC II

Presents exogenous antigens on immune cells

Antibody function

Neutralization, opsonization, complement activation, and agglutination

IgM

First antibody produced in response to infection

IgG

Most abundant antibody in blood and provides long-term immunity

IgA

Found in mucosal areas like saliva and mucus

IgE

Involved in allergic responses and parasites

Vaccination

Administration of vaccine to stimulate immune response

Immunization

Body's response to vaccination or infection

Natural active immunity

Immunity from infection

Natural passive immunity

Antibodies from mother (placenta or milk)

Artificial active immunity

Immunity from vaccination

Artificial passive immunity

Receiving antibodies from another source

Killed vaccine

Inactivated pathogen that cannot replicate

Live attenuated vaccine

Weakened pathogen that produces strong immunity

Subunit vaccine

Uses parts of pathogen (proteins)

DNA vaccine

Uses genetic material to produce antigen in host cells

Herd immunity

Population-level protection when enough individuals are immune

Chain of infection

Agent, reservoir, exit, transmission, entry, host

Reservoir

Location where pathogen lives and persists

Mode of transmission

How pathogen spreads (contact, airborne, vector, etc.)

Vector

Living organism that transmits disease

Zoonosis

Disease transmitted from animals to humans

Incubation period

Time between exposure and symptom onset

Prodromal stage

Early mild symptoms

Period of invasion

Peak of infection with most severe symptoms

Convalescent period

Recovery stage

Acute disease

Short-term illness

Chronic disease

Long-lasting illness

Latent disease

Disease that can reactivate later

Incidence

Number of new cases in a population

Prevalence

Total number of cases in a population

Morbidity rate

Rate of disease in a population

Mortality rate

Death rate in a population

ID50

Number of microbes required to infect 50% of population

Primary pathogen

Causes disease in healthy individuals

Opportunistic pathogen

Causes disease when host defenses are weakened

Nosocomial infection

Hospital-acquired infection

Koch's postulates

Steps used to identify causative agent of disease

Communicable disease

Disease that can spread between individuals

Noncommunicable disease

Disease not spread between individuals

Contagious disease

Highly transmissible disease

Asymptomatic carrier

Individual who spreads disease without symptoms

Endemic

Disease consistently present in a population

Epidemic

Disease occurrence above expected levels

Pandemic

Global spread of disease