Lecture Notes Vocabulary Flashcards: Host Defenses, Immunity, and Pathogens

A comprehensive set of vocabulary flashcards covering innate and adaptive immunity, key immune cells, infectious diseases, pathogens, virulence factors, and notable clinical concepts from the lecture notes.

Innate immune system

The nonspecific first line of defense that blocks invasion at portals of entry and includes physical barriers, chemical barriers, and nonspecific internal defenses.

First line of defense

Physical and chemical barriers that block entry of pathogens (e.g., skin, mucous membranes, acids, lysozyme).

Physical barriers

Skin and mucous membranes that resist entry; layers slough off and blinking/ciliary action impede microbes.

Microbiota (microbial antagonism)

Resident microbes that block pathogen access and create environments unfavorable to invaders.

Chemical barriers

Salt, low pH, stomach acid, lysozyme, and other antimicrobial substances that deter pathogens.

Second line of defense

Internal nonspecific defenses such as phagocytosis, inflammation, fever, and antimicrobial proteins.

Third line of defense (adaptive immunity)

Specific immunity involving B and T lymphocytes with memory for future encounters.

Neutrophil

Short-lived granulocyte that engulfs and kills bacteria during bacterial infections.

Basophil

Granulocyte involved in inflammatory responses via mediator release.

Eosinophil

Granulocyte that targets parasites and participates in allergic/inflammatory responses.

Monocyte

Circulating precursor that becomes macrophages or dendritic cells; phagocytic.

Macrophage

Tissue phagocyte that kills microbes and presents antigens to T cells.

Dendritic cell

Antigen-presenting cell crucial for activating T cells.

T cell

Lymphocyte involved in cell-mediated immunity; includes CD4 helper and CD8 cytotoxic subsets.

B cell

Lymphocyte that differentiates into plasma cells to secrete antibodies and can present antigen.

Natural killer (NK) cell

Lymphocyte that destroys virally infected and tumor cells without prior sensitization.

Gamma-delta T cell

T cell subtype with NK-like activity that responds to certain antigens and PAMPs.

Phases of phagocytosis

Chemotaxis → adhesion → engulfment → phagosome formation → phagolysosome formation → killing → debris release.

Chemotaxis

Movement of phagocytes toward chemical signals at the injury site.

PAMP

Pathogen-associated molecular pattern recognized by host immune receptors.

PRR

Pattern recognition receptor that detects PAMPs on pathogens.

Phagosome

Vacuole formed after a microbe is engulfed by a phagocyte.

Phagolysosome

Phagosome fused with a lysosome for degradation of its contents.

Interferon

Antiviral cytokine produced by leukocytes in response to infection; induces antiviral genes.

Antiviral activity of interferons

Interferons stimulate cells to express antiviral proteins that limit viral replication.

Complement system

Cascade of plasma proteins that enhances immunity through opsonization, inflammation, and lysis; pathways include classical, lectin, and alternative.

Classical pathway

Complement activation triggered by antibody–antigen complexes.

Lectin pathway

Complement activation triggered by lectins binding microbial sugars not found in humans.

Alternative pathway

Complement activation initiated on microbial surfaces without antibodies.

Antigen

Substance that elicits an immune response; often a protein or polysaccharide.

Epitope

Specific region of an antigen recognized by immune receptors.

Hapten

Small molecule that becomes antigenic when bound to a larger carrier protein.

Antigen-presenting cell (APC)

Cell that processes and presents antigen fragments to T cells (e.g., dendritic cells, macrophages, B cells).

CD4 T cell

Helper T cell; coordinates immune responses and supports other immune cells.

CD8 T cell

Cytotoxic T cell; destroys virally infected or abnormal cells.

Memory T cell

Long-lived T cell that responds rapidly upon re-exposure to the same antigen.

Activated cytotoxic T cell

CD8 T cell that kills infected host cells and forms memory cytotoxic cells.

Activated helper T cell

CD4 T cell that activates B cells and CD8 T cells and helps form memory helper cells.

Plasma cell

Differentiated B cell that secretes antibodies.

Memory B cell

Long-lived B cell that responds quickly on re-exposure to the antigen.

IgA

Antibody found in secretions and colostrum; protects mucosal surfaces and infant gut.

IgD

Monomer antibody found on B cells; least circulated antibody.

IgE

Antibody involved in allergic responses and defense against parasites.

IgG

Dominant circulating antibody; crosses placenta; long half-life; neutralizes toxins.

IgM

First antibody produced in response to infection; pentameric form; produced by fetus.

Natural active immunity

Infection with a pathogen leading the body to produce its own antibodies.

Natural passive immunity

Maternal antibodies transferred to the fetus/infant via placenta or breast milk.

Artificial active immunity

Immunity from vaccination; exposure to antigen induces antibody production.

Artificial passive immunity

Administration of preformed antibodies for immediate, temporary protection.

Necrotizing fasciitis

Rapidly spreading infection of fascia and soft tissue; often caused by Streptococcus pyogenes; requires surgical debridement.

Streptococcus pyogenes

Group A Streptococcus; common cause of necrotizing fasciitis; virulence factors include M protein, streptolysins.

M protein

S. pyogenes surface protein that helps resist phagocytosis.

Hyaluronidase

Enzyme that degrades tissue to facilitate spread of infection.

Streptokinase

Enzyme that dissolves clots to promote microbial spread.

Capsule (S. pyogenes)

Polysaccharide layer enhancing resistance to phagocytosis.

Varicella zoster virus (VZV)

Varicella (chickenpox) virus; establishes latency and can reactivate as shingles.

Shingles

Reactivation of latent VZV infection in a dermatomal distribution.

Koplik spots

Pathognomonic oral lesions seen in measles.

Measles virus

Rubeola; highly contagious, airborne; prevented by MMR.

MMR vaccine

Vaccine protecting against measles, mumps, and rubella.

Rubella virus

Rubella virus; can cause congenital rubella syndrome.

Congenital rubella syndrome (CRS)

Fetal abnormalities from rubella infection during pregnancy.

Meningitis

Inflammation of the meninges with symptoms like photophobia and stiff neck; common pathogens include N. meningitidis, S. pneumoniae, H. influenzae, Listeria monocytogenes.

Creutzfeldt-Jakob disease

Prion disease causing rapid neurodegeneration; no cure.

Prion

Misfolded protein that propagates disease (transmissible spongiform encephalopathy).

Rabies virus

Neurotropic virus causing fatal encephalitis; transmitted via bites or exposure.

Milwaukee Protocol

Experimental rabies treatment involving induced coma and antivirals; not reliably successful.

Tetanus

Clostridium tetani infection causing muscle rigidity and spastic paralysis via tetanospasmin toxin.

Tetanospasmin

Neurotoxin that inhibits inhibitory neurotransmitter release, causing spasms.

Clostridium tetani

Bacterium that causes tetanus; spore-forming anaerobe.

Wound botulism

Botulinum toxin exposure from wound infection causing flaccid paralysis.

Clostridium botulinum

Bacterium producing botulinum toxin; causes foodborne and wound botulism.

Sepsis

Systemic inflammatory response to infection; may lead to septic shock.

COVID-19

Disease caused by SARS-CoV-2; can trigger cytokine storm and multi-system effects.

SARS-CoV-2

Coronavirus causing COVID-19; uses ACE2 receptor to enter cells.

ACE2

Host receptor used by SARS-CoV-2 for cell entry.

Endocarditis

Infection of heart valves; risk factors include dental procedures, IV drug use; causative agents include Staphylococcus aureus and Streptococcus species.

Borrelia burgdorferi

Spirochete bacterium causing Lyme disease; transmitted by Ixodes tick.

OspA

Outer surface protein A of Borrelia burgdorferi; aids in survival in tick and early infection.

OspC

Outer surface protein C of Borrelia burgdorferi; important in mammalian infection.

Antigenic variation (Lyme)

Variation in Borrelia surface proteins to evade immune detection.

Tick vector

Ixodes tick that transmits Borrelia burgdorferi; hosts include mice and small mammals.

Lyme disease

Infection by Borrelia burgdorferi; presents with erythema migrans (bull’s-eye rash) and possible systemic symptoms.

DTaP/Tdap/Td

Vaccines for diphtheria, tetanus, and pertussis; recommended in pregnancy (Tdap) and for boosters.

HIV

Human immunodeficiency virus; targets CD4 T cells; undergoes reverse transcription and integration, leading to progressive immune failure.

AIDS

Acquired immunodeficiency syndrome; defined by CD4 count <200 cells/mm3 or AIDS-defining illnesses.

Pharyngitis

Sore throat; can be viral or bacterial; bacterial cause includes Streptococcus pyogenes and Fusobacterium necrophorum.

Streptococcus pyogenes

Group A Streptococcus; causes pharyngitis and other infections; virulence factors include M protein and streptolysins.

Fusobacterium necrophorum

Anaerobic bacterium causing pharyngitis and Lemierre’s syndrome.

Lemierre’s syndrome

Septic thrombophlebitis of the internal jugular vein following oropharyngeal infection.

Influenza

Enveloped, segmented, negative-sense RNA virus with types A, B, C; stained by hemagglutinin and neuraminidase; subject to drift and shift.

Hemagglutinin

Influenza surface protein that binds host receptors to enable entry.

Neuraminidase

Influenza enzyme cleaving sialic acid to release new virions and aid spread.

Antigenic drift

Small, gradual mutations in viral antigens; reduces memory cell recognition.

Antigenic shift

Major genetic reassortment leading to new pandemic strains.

Mycobacterium tuberculosis

Bacterium causing TB; acid-fast; forms granulomas with latency and possible reactivation.

Mycolic acid

Waxy cell wall component of M. tuberculosis that resists digestion by phagocytes.

Cord factor

Virulence factor in M. tuberculosis; inhibits phagosome-lysosome fusion.

RIPE therapy

Rifampin, Isoniazid, Pyrazinamide, Ethambutol—standard TB treatment.

Directly observed therapy (DOT)

Treatment strategy where healthcare workers observe patients taking TB meds.