Cells of the Immune System – Vocabulary Flashcards

Vocabulary flashcards covering key terms, cell types, molecules, and processes introduced in the lecture on classification, structure, and function of cells in the immune system.

Leukocytes

White blood cells; cellular components of the immune system derived from haematopoietic stem cells.

Lymphoid Lineage

Developmental pathway giving rise to lymphocytes (B, T, NK cells).

Myeloid Lineage

Developmental pathway producing granulocytes, monocytes/macrophages, dendritic cells, mast cells, and others.

Innate Immunity

Rapid, non-specific arm of immunity involving cells such as neutrophils, macrophages, NK cells, etc.

Adaptive Immunity

Specific, memory-forming arm of immunity mediated by B and T lymphocytes.

Granulocytes

Leukocytes containing cytoplasmic granules; include neutrophils, eosinophils, basophils, mast cells.

Agranulocytes

Leukocytes lacking prominent granules; include lymphocytes, monocytes, macrophages, dendritic cells.

Phagocytosis

Endocytic process—adherence, ingestion, digestion, exocytosis—used by phagocytes to destroy particles.

Phagocyte

Cell capable of phagocytosis (e.g., neutrophil, macrophage, dendritic cell, eosinophil).

Professional Antigen-Presenting Cell (APC)

Cell that presents antigen via MHC II to T cells; mainly dendritic cells, macrophages, B cells.

Antigen Presentation

Display of processed antigenic peptides on MHC molecules for T-cell recognition.

Cell-Mediated Cytotoxicity

Killing of infected or abnormal cells by cytotoxic T lymphocytes or NK cells via apoptosis.

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

Destruction of antibody-coated targets by Fc-receptor-bearing cells (NK, macrophages, neutrophils, eosinophils).

Neutrophils

Most abundant granulocytes (50-70%); first responders that perform phagocytosis and release NETs.

Primary (Azurophilic) Granules

Larger neutrophil granules containing peroxidase, lysozyme, hydrolytic enzymes.

Secondary (Specific) Granules

Smaller neutrophil granules with collagenase, lactoferrin, lysozyme, NADPH oxidase.

Neutrophil Extracellular Traps (NETs)

Web-like DNA/protein structures released by neutrophils to trap microbes.

Monocytes

Circulating precursors that exit blood after ~8 h and differentiate into macrophages or dendritic cells in tissues.

Macrophages

Tissue phagocytes derived from monocytes; perform phagocytosis and antigen presentation.

Resident Macrophages

Macrophages permanently present in tissues (e.g., Kupffer cells, mesangial cells) with specialized roles.

Kupffer Cells

Resident macrophages of the liver involved in tissue repair and clearance of debris.

Mesangial Cells

Resident kidney macrophages participating in glomerular filtration maintenance.

Dendritic Cells

Potent professional APCs that capture antigen, mature, and migrate to lymph nodes to activate T cells.

MHC Class II

Molecules on professional APCs presenting exogenous peptides to CD4+ T helper cells.

Eosinophils

1-3% of leukocytes; granulocytes that release toxic proteins and free radicals, fight parasites, mediate allergy, and perform ADCC via IgE.

Basophils

Mast Cells

Tissue-resident granulated cells; release histamine and cytokines—central to allergic reactions and inflammation.

Histamine

Vasoactive amine in basophil and mast cell granules; increases vascular permeability during inflammation.

Natural Killer (NK) Cells

Innate lymphocytes (5-10% of circulating lymphocytes) that kill infected or cancerous cells lacking normal MHC I.

Missing-Self Recognition

NK-cell mechanism detecting reduced MHC I on target cells, triggering cytotoxicity.

Activating Receptors (NK)

Surface molecules recognising stress ligands on abnormal cells, initiating NK-cell killing.

Inhibitory Receptors (NK)

Surface molecules recognising normal MHC I, preventing NK-cell attack on healthy cells.

Perforin

Protein in NK and CTL granules forming pores in target-cell membranes.

Granzymes

Serine proteases entering target cells via perforin pores to trigger apoptosis.

Fas-Dependent Cytotoxicity

Apoptosis induced by interaction of Fas ligand (on NK/CTL) with Fas receptor on target cells.

Fas-Independent Cytotoxicity

Perforin/granzyme-mediated apoptosis executed by NK cells or CTLs without Fas engagement.

Apoptosis

Programmed cell death involving caspase cascade, mitochondrial disruption, and DNA fragmentation.

Necrosis

Uncontrolled cell death characterized by membrane rupture and inflammation, unlike apoptosis.

B Lymphocytes (B Cells)

Adaptive immune cells maturing in bone marrow; produce antibodies and act as APCs.

T Lymphocytes (T Cells)

Adaptive immune cells maturing in thymus; subdivided into CD4+ helper and CD8+ cytotoxic subsets.

B-Cell Receptor (BCR)

Membrane-bound immunoglobulin on B cells recognizing diverse antigens directly.

T-Cell Receptor (TCR)

Heterodimeric receptor on T cells recognising peptide antigens presented by MHC molecules.

Plasma Cell

Effector B cell that secretes large amounts of specific antibodies; short-lived except memory precursors.

CD4+ T Helper Cell

T lymphocyte subset coordinating immune responses by secreting cytokines upon MHC II recognition.

CD8+ Cytotoxic T Lymphocyte (CTL)

T cell subset inducing apoptosis of infected cells presenting peptide on MHC I.

Positive Selection (T Cells)

Thymic process ensuring T cells recognise self-MHC molecules weakly enough to survive.

Negative Selection (T Cells)

Thymic elimination of T cells with high affinity for self-antigens, establishing central tolerance.

Haematopoietic Stem Cell

Multipotent bone-marrow precursor that gives rise to all blood and immune cells.