Leukocytes & Inflammation – Cellular Components of the Immune System

Vocabulary flashcards summarizing key cells, mediators, and mechanisms discussed in the lecture on leukocytes and inflammation.

Hematopoietic Stem Cell (HSC)

Pluripotent bone-marrow stem cell that gives rise to all blood cells, including all leukocytes.

Common Myeloid Progenitor

HSC-derived precursor that produces granulocytes, monocytes/macrophages, dendritic cells, mast cells, erythrocytes, and platelets.

Common Lymphoid Progenitor

HSC-derived precursor that produces B cells, T cells, NK cells, and some dendritic cells.

Neutrophil

Most abundant granulocyte (40–75% of leukocytes); rapid phagocyte that kills bacteria via phagocytosis, degranulation, and NET release.

Macrophage

Mononuclear phagocyte that performs phagocytosis, bactericidal activity, cytokine secretion, and antigen presentation.

Monocyte

Blood precursor of macrophages and some dendritic cells; enters tissues and differentiates.

Dendritic Cell

Professional antigen-presenting cell that captures antigens in peripheral tissues and presents them to T cells in lymph nodes.

Eosinophil

Granulocyte specialized in killing antibody-coated parasites by releasing toxic granule proteins and lipid mediators.

Basophil

Rare granulocyte (<1%); releases histamine-rich granules in allergic and parasitic responses; exact functions still being defined.

Mast Cell

Tissue-resident cell that releases preformed histamine, heparin, and newly synthesized lipid mediators to drive inflammation and allergy.

Natural Killer (NK) Cell

Innate lymphoid cell that kills virus-infected or tumor cells lacking MHC-I via perforin/granzyme or FasL pathways.

CD8+ Cytotoxic T Cell

Adaptive lymphocyte that recognizes antigen on MHC-I and kills infected or malignant cells using perforin, granzymes, or FasL.

CD4+ Helper T Cell

Adaptive lymphocyte that orchestrates immune responses by secreting cytokines; includes TH1 and TH2 subsets.

TH1 Cell

CD4 subset that promotes cell-mediated immunity, activating macrophages and opsonizing IgG production.

TH2 Cell

CD4 subset that promotes humoral immunity, driving B-cell activation and class switching to IgE/IgA.

γδ T Cell

T-cell subset with γδ TCR; participates in early responses and immune regulation.

Antigen-Presenting Cell (APC)

Cell (e.g., dendritic cell, macrophage, B cell) that processes and presents antigenic peptides on MHC molecules to T cells.

Phagocytosis

Three-step process (recognition/adherence, engulfment, intracellular killing) by which cells ingest and destroy microbes.

Pattern-Associated Molecular Pattern (PAMP)

Conserved microbial structure recognized by innate receptors such as Toll-like receptors (TLRs).

Toll-Like Receptor (TLR)

Innate membrane receptor that binds PAMPs and triggers phagocyte activation and inflammation.

Diapedesis

Extravasation process whereby leukocytes migrate out of blood vessels into tissues.

Chemotaxis

Directed cell movement toward increasing concentrations of chemokines or other chemoattractants.

Degranulation

Rapid exocytosis of cytotoxic or inflammatory granule contents by neutrophils, eosinophils, basophils, or mast cells.

Neutrophil Extracellular Trap (NET)

Web-like DNA structure studded with antimicrobial proteins released by neutrophils to trap and kill microbes extracellularly.

Perforin

Pore-forming protein released by cytotoxic lymphocytes that allows granzymes to enter target cells.

Granzyme

Serine protease delivered into target cells by perforin to activate caspases and induce apoptosis.

Fas–Fas Ligand Pathway

Cell-surface death-receptor interaction that triggers target-cell apoptosis, used by cytotoxic T cells and NK cells.

Opsonization

Coating of pathogens with antibodies or complement to enhance phagocytosis.

Neutralization

Antibody action that blocks microbial toxins or viral attachment, preventing infection or toxicity.

Complement Activation

Antibody-triggered enzymatic cascade that leads to pathogen lysis, opsonization, and inflammation.

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

Killing of antibody-coated target cells by NK cells, macrophages, or eosinophils through Fc-receptor engagement.

Myeloperoxidase

Heme enzyme in neutrophil and macrophage azurophilic granules that produces hypochlorous acid for microbial killing.

Defensins

Cationic antimicrobial peptides stored in neutrophil granules that disrupt microbial membranes.

Major Basic Protein (MBP)

Toxic cationic protein in eosinophil granules that kills parasites and triggers mast-cell histamine release.

Histamine

Preformed mast-cell and basophil mediator that increases vascular permeability and smooth-muscle contraction.

Platelet-Activating Factor (PAF)

Lipid mediator produced by eosinophils and mast cells that induces bronchoconstriction and leukocyte chemotaxis.

Lactoferrin

Iron-binding protein in neutrophil specific granules that deprives bacteria of iron.

Colony-Stimulating Factors (CSF)

Cytokines (e.g., GM-CSF) that stimulate bone-marrow production of specific leukocyte lineages.

Oxygen-Dependent Killing

Intracellular killing mechanism using reactive oxygen species produced by NADPH oxidase in phagocytes.

Inflammation

Protective tissue response characterized by redness, heat, swelling, pain, and loss of function, driven by leukocyte mediators.