• Antigen (Ag):any substance that triggers (generates) the immune system to produce antibodies against it, in immunology an antigen is a molecule/molecular structure present on the outside of a pathogen

• Antibody: aka, immunoglobulin, a protein used by the immune system to identify and neutralise foreign objects e.g. bacteria, virus... recognises unique molecule of the pathogen (the Ag). Neutralising antibody (also see monoclonal antibody therapy)

• Innate (within hours): epithelial barriers, macrophages, phagocytes, dendritic cells, complement, NK cells)

• Adaptive (within days):

  • Humoral (relating to body fluids, free-floating antibodies produced by B lymphocytes)

  • Cell-mediated (response is carried out by cytotoxic cells: T lymphocytes>effector T cells

• Cytokines (chemokines, interferons, interleukins, tumour necrosis factors...), proteins produced by a range of cells, moderate humoral/cell-based immune/host response to infection, inflammation, cancer etc. Cytokine storm (oversecretion), ?mechanism of lung damage, dysfunction coagulation in COVID-19, death in the 1918 Spanish flu. (monoclonal antibody therapies can bind and inhibit various cytokines e.g. IL-6, TNF)

White blood cells

• AKA leucocytes

• Cells of the immune system, found throughout body including blood & lymphatic system, produced by hematopoietic stem cells in bone marrow

• Classified by cell lineage (rather than physical characteristics: granulo/agranulocytes):

  • Myeloid cells: neutrophils, eosinophils, mast cells, basophils, monocytes (dendritic cells, macrophages) *neutrophils/monocytes are phagocytic (Greek: eat cell)

  • Lymphoid cells: T-cells (helper, memory, cytotoxic), B-cells (plasma, memory), natural killer cells