Responding to Antigens – Key Vocabulary

A comprehensive set of vocabulary flashcards covering pathogens, barrier defences, innate immune components, key molecules and inflammatory processes from the lecture on responding to antigens.

Disease

Any harmful deviation from the normal structural or functional state of an organism.

Pathogen

An agent capable of causing disease.

Cellular pathogen

A living, cell-based pathogen such as bacteria, fungi, protists or parasitic animals.

Non-cellular pathogen

A non-living infectious agent such as a virus, viroid or prion.

Virus

A non-cellular pathogen that replicates only inside a host cell using the host’s machinery.

Viroid

A small circular RNA molecule that infects plants; lacks a protein coat.

Prion

An infectious misfolded protein that induces abnormal folding of normal proteins, especially in the brain.

Bacterium

A unicellular prokaryotic microorganism; a common cellular pathogen.

Fungus

A eukaryotic organism (unicellular or multicellular) that can act as a cellular pathogen.

Protist

A diverse group of mostly unicellular eukaryotes; some are pathogenic.

Physical barrier (animal)

Structure that blocks pathogen entry, e.g. intact skin, mucous membranes, cilia.

Chemical barrier (animal)

Molecules that inhibit or destroy pathogens, e.g. lysozyme in tears, stomach acid, acidic sweat.

Microbiota barrier

Non-pathogenic normal flora that outcompete potential pathogens for space and nutrients.

Intact skin

Continuous external layer that forms a primary physical barrier to infection.

Mucous membrane

Epithelial layer secreting mucus that traps pathogens; cilia sweep them away.

Lysozyme

Enzyme in tears, saliva, etc. that degrades bacterial cell walls.

Stomach acid

Highly acidic gastric secretion that kills ingested pathogens.

Normal flora

Resident non-pathogenic microbes that inhibit growth of pathogenic species.

Plant physical barrier

Structural feature preventing pathogen entry, e.g. thick bark, waxy cuticle.

Waxy cuticle

Hydrophobic layer on leaves that impedes pathogen penetration and water loss.

Lignin

Complex polymer that strengthens plant cell walls, creating a barrier to pathogens.

Callose

Polysaccharide deposited in plant cell walls to seal off infection sites.

Plant chemical barrier

Toxins or enzymes produced by plants that harm pathogens or deter herbivores.

Chitinase

Plant enzyme with antifungal properties that degrades fungal cell walls.

Phenols (plant)

Chemical compounds secreted by wounded plants that repel or kill microbes.

Defensins

Small antimicrobial peptides in plants toxic to microbes and fungi.

Saponins

Plant compounds that disrupt fungal cell membranes.

Innate immune response

Rapid, non-specific defence present from birth; includes first and second lines of defence.

Leukocyte

A white blood cell produced in bone marrow that participates in immune responses.

Mast cell

Tissue-resident leukocyte that releases histamine during inflammation and allergic reactions.

Macrophage

Large phagocytic leukocyte that engulfs pathogens and presents antigens via MHC II.

Dendritic cell

Professional antigen-presenting cell that phagocytoses pathogens and migrates to lymph nodes.

Neutrophil

Abundant, short-lived phagocyte; first responder that forms pus and releases antimicrobial chemicals.

Eosinophil

Leukocyte that releases toxic granules against large parasites and contributes to allergies.

Natural killer (NK) cell

Lymphocyte that recognises missing or altered MHC I and induces apoptosis in cancerous or virus-infected cells.

Antigen

Any substance capable of triggering an immune response; often a protein with a unique structure.

Self-antigen

Molecule produced by the body, recognised as ‘self’ by the immune system.

MHC class I

Self marker on all nucleated cells used to display endogenous peptides to immune cells.

Cytokine

Signalling molecule that coordinates immune cell communication, e.g. interferons.

Interferon

Type of cytokine released by virus-infected cells that limits viral replication and boosts MHC I expression.

Complement proteins

Plasma proteins that enhance pathogen detection, attract phagocytes, opsonise microbes and can cause lysis.

Inflammation

Localized response with redness, heat, swelling and pain that increases blood flow and leukocyte access.

Histamine

Chemical released by mast cells causing vasodilation and increased vascular permeability during inflammation.

Allergen

Harmless antigen that elicits an excessive immune (often inflammatory) response.

Pyroptosis

Inflammatory form of programmed cell death where the membrane ruptures, releasing cytokines.

Phagocytosis

Process by which cells engulf and digest pathogens or debris.