Introduction to Immunology – Key Terminology

Vocabulary flashcards covering major pathogens, immune organs, cell types, molecules, and fundamental immunological processes as outlined in the lecture notes.

Pathogens

Biological agents (viruses, bacteria, fungi, parasites) capable of causing disease.

Enveloped Virus

Virus surrounded by a lipid membrane that aids entry and can be targeted by antibodies and complement.

Non-enveloped Virus

Virus lacking a lipid envelope; relies on capsid proteins for cell entry and is generally more resistant to environmental stress.

Gram-positive Bacterium

Bacterium with a thick peptidoglycan cell wall that retains crystal-violet stain; often susceptible to lysozyme and certain antibiotics.

Gram-negative Bacterium

Bacterium possessing a thin peptidoglycan layer and outer membrane containing lipopolysaccharide (endotoxin); stains pink with Gram stain.

Intracellular Bacterium

Bacterium that survives and replicates inside host cells, evading many extracellular immune mechanisms (e.g., Mycobacterium tuberculosis).

Extracellular Bacterium

Bacterium that lives outside host cells and is mainly targeted by complement, antibodies, and phagocytes.

Fungi

Eukaryotic organisms (yeasts, hyphae, spores) that provoke innate responses (NETosis, complement) and Th1-mediated immunity.

Parasites

Protozoa or helminths that elicit IgE, eosinophil, mast-cell, and Th2 immune responses.

Bone Marrow

Primary lymphoid organ where all blood cells originate and B cells mature.

Thymus

Primary lymphoid organ in which T cells mature and undergo positive and negative selection.

Lymph Node

Secondary lymphoid organ that filters lymph, presents antigen, and facilitates T–B cell interactions.

Spleen

Secondary lymphoid organ that filters blood, removes aged erythrocytes, and mounts responses to blood-borne pathogens.

MALT (Mucosa-Associated Lymphoid Tissue)

Diffuse lymphoid tissues (e.g., Peyer’s patches, tonsils) guarding mucosal surfaces against pathogens.

Neutrophil

Most abundant granulocyte; phagocytic first responder that can perform NETosis and release antimicrobial granules.

Monocyte

Circulating precursor that differentiates into macrophages or dendritic cells in tissues.

Macrophage

Phagocytic tissue cell that presents antigen, produces cytokines, and orchestrates inflammation.

Dendritic Cell

Professional antigen-presenting cell that links innate and adaptive immunity by activating naïve T cells.

Eosinophil

Granulocyte specialized for combating parasites and contributing to allergic inflammation.

Basophil

Circulating granulocyte that releases histamine and participates in IgE-mediated responses.

Mast Cell

Tissue-resident granulocyte that releases histamine and other mediators upon IgE cross-linking, driving allergy and parasite defense.

NK Cell

Innate lymphocyte that recognizes missing-self (low MHC I) and mediates cytotoxicity via perforin-granzyme and ADCC.

B Lymphocyte

Adaptive immune cell bearing BCR; differentiates into antibody-secreting plasma cells and memory B cells.

T Lymphocyte

Adaptive immune cell bearing TCR; subdivided into CD4 helper and CD8 cytotoxic subsets.

TH1 Cell

CD4 T helper subset producing IFN-γ to activate macrophages and defend against intracellular pathogens.

TH2 Cell

CD4 T helper subset producing IL-4, IL-5, IL-13 to stimulate eosinophils, IgE, and defense against parasites.

TC (CD8) Cell

Cytotoxic T lymphocyte that kills infected or malignant cells through perforin-granzyme-mediated apoptosis.

Pattern-Recognition Receptor (PRR)

Innate receptor (e.g., TLR, NOD) that detects conserved microbial motifs inside cells or on membranes.

Complement System

Cascade of plasma proteins that opsonize microbes, generate anaphylatoxins, and form the membrane-attack complex.

Fc Receptor

Cell-surface molecule that binds the Fc region of antibodies, enabling phagocytosis or ADCC.

Complement Receptor

Receptor on phagocytes that recognizes complement fragments (e.g., CR1 binding C3b) to enhance uptake.

Cytokine

Small, soluble protein mediator that regulates immunity, inflammation, and hematopoiesis.

Chemokine

Cytokine subclass that directs cell migration along concentration gradients.

MHC Class I

Molecule on all nucleated cells presenting endogenous peptides to CD8 T cells.

MHC Class II

Molecule on professional APCs presenting exogenous peptides to CD4 T cells.

B Cell Receptor (BCR)

Membrane-bound immunoglobulin that recognizes native antigen on B cells.

Antibody

Secreted immunoglobulin that neutralizes, opsonizes, and activates complement against antigens.

T Cell Receptor (TCR)

Heterodimeric receptor recognizing peptide–MHC complexes on T cells.

CD4 Molecule

Co-receptor on helper T cells that binds MHC II and assists signaling.

CD8 Molecule

Co-receptor on cytotoxic T cells that binds MHC I and enhances activation.

Cytotoxicity (Apoptosis)

Target-cell death induced by NK or CD8 T cells via perforin and granzymes.

Antibody-Dependent Cellular Cytotoxicity (ADCC)

Killing of antibody-coated cells by NK cells through FcγR engagement.

Phagocytosis

Engulfment and intracellular digestion of microbes by neutrophils or macrophages.

Opsonisation

Tagging of pathogens with antibodies or complement to enhance phagocytosis.

Neutralisation

Antibody binding that blocks pathogen attachment or toxin activity.

Inflammation

Coordinated vascular and cellular response to injury or infection, producing redness, heat, swelling, and pain.

Complement Activation

Sequential proteolysis of complement components via classical, lectin, or alternative pathways, culminating in microbial lysis.

Antigen Presentation

Display of peptide–MHC complexes by APCs to T cells, initiating adaptive immunity.

T and B Cell Activation

Process whereby antigen receptor engagement and co-stimulation trigger lymphocyte proliferation and differentiation.

Antibody/BCR/TCR Diversity

Generation of vast receptor repertoires through V(D)J recombination and, for antibodies, somatic hypermutation.