Cell Biology, Haematology and Immunology - Innate Immunity Vocabulary

A complete set of vocabulary flashcards covering innate immune host defenses, immune cell lineages, pattern recognition mechanisms, and complement pathways based on the lecture notes.

Innate Immunity

The non-specific first line of defence providing passive protection with a rapid response (from immediate exposure to $12\text{ hours}$) against common structures on microbes without developing immunological memory.

Adaptive Immunity

A receptor-driven, highly specific immune response that develops over time and provides long-lasting protection through immunological memory.

Avoidance

An anatomical line of defence used to prevent contact with or entry of microorganisms into the host.

Resistance

A line of defence involving the triggering of cellular or molecular effector mechanisms to destroy pathogens.

Tolerance

A line of defence that enhances the host's capacity to resist damage caused by pathogens or immune responses.

Commensal Organisms

Microorganisms that colonize host cells where one organism benefits while the other is neutral, or both benefit (mutualistic), supporting immunity by preventing pathogen adhesion and colonization.

PAMPs (Pathogen-Associated Molecular Patterns)

Conserved molecular structures expressed on the outside of microbes that are necessary for microbial survival and are recognised by host pattern recognition receptors.

DAMPs (Damage-Associated Molecular Patterns)

Host-derived molecules released from damaged, dying, or infected cells following chemical toxins, infection, or trauma to signal cell injury.

Alarmin

A specific type of DAMP released by healthy host cells to enhance and amplify the innate immune response to infection.

Pattern Recognition Receptors (PRRs)

Receptors present on immune cells (such as macrophages, neutrophils, dendritic cells) and in blood or mucus that recognize PAMPs and DAMPs to initiate downstream signaling.

Toll-Like Receptors (TLRs)

Inherited pattern recognition receptors located on the plasma and endosomal membranes of phagocytes, dendritic cells, B cells, and endothelial cells that detect specific microbial components.

Pluripotent Hematopoietic Stem Cell

A self-renewing stem cell located in the bone marrow that gives rise to common lymphoid progenitors and common myeloid progenitors, generating all blood and immune cell lineages.

Neutrophils

The most abundant circulating phagocytes present at the earliest phase of infection that kill via phagocytosis and contain primary granules with defensins and secondary granules with lysozyme.

Macrophages

Long-lived phagocytic cells derived from monocytes or fetal development whose production is modified by M-CSF; they ingest pathogens and apoptotic cells, secrete cytokines/chemokines, present antigens, and promote tissue repair.

Dendritic Cells

Key antigen-presenting cells featuring long cytoplasmic extensions that populate epithelial and lymphoid tissues, express high levels of PRRs, and present captured antigens to lymphocytes.

Natural Killer (NK) Cells

Cytotoxic lymphocytes constituting over $15\%$ of blood cells that kill virus-infected and tumor cells and secrete cytokines such as $\text{IFN-}\gamma$.

Mast Cells

Bone marrow-derived tissue cells located in skin and mucosal membranes that release histamine, heparin, cytokines, and proteolytic enzymes to mediate inflammation, vasodilation, and allergic reactions.

Phagocytosis

The multi-step cellular process by which phagocytes engulf and digest particulate matter $\ge 0.5\,\mu\text{m}$, involving chemotaxis, pseudopod extension, phagosome formation, phagolysosome fusion, and enzyme degradation.

Complement System

A network of approximately $30$ soluble plasma proteins that operate through three activation pathways (Classical, Lectin, Alternative) to promote opsonisation, recruitment of phagocytes, and pathogen lysis.

C3 Convertase

An enzymatic complex generated by all complement pathways that cleaves $C3$ into $C3a$ (which recruits phagocytes and activates mast cells) and $C3b$ (which binds microbial surfaces for opsonisation).

C5 Convertase

An enzyme complex formed in complement pathways that cleaves $C5$ into $C5a$ (a chemotactic agent for neutrophils and monocytes) and $C5b$.

Membrane Attack Complex (MAC)

A pore-forming complex generated by complement proteins $C5b$, $C6$, $C7$, $C8$, and $C9$ that inserts into the lipid bilayer of host or microbial membranes, causing osmotic swelling and cell lysis.

Lectin Pathway

An innate complement activation pathway initiated when Mannose-binding lectin (MBL) or ficolins bind specific carbohydrates on pathogen surfaces.

Alternative Pathway

An innate complement activation pathway triggered by the spontaneous hydrolysis of $C3$ into $\text{C3(H}_2\text{O)}$, resulting in the deposition of C3 convertase directly on microbial surfaces.

Inflammation

A local protective response characterized by increased local blood supply, emigration of leukocytes into tissue, and increased vascular permeability triggered when pathogens breach host protective barriers.