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> Innate Immediate but non-specific WY Adaptive 7-10 days but specific A Simplified Guide to the Immune System Natural Killer (NK) cells activated by cytokines and identify tumour or virally infected cells. NK cell binds and releases enzymes. into the cell causing apoptosis cytokines calling for help. Pathogen penetrates physical barriers and enters body Macrophage (specialised monocyte) in tissue detects and engulfs pathogen (phagocytosis) Macrophage processes and presents antigen and produces ‘Other macrophages, neutrophils (also a phagocyte which is very effective but short-lived), dendritic cells and granulated cells drawn in from the blood stream (example of chemotaxis) Granulated Basophil Cells (circulate) and Mast Cells (resident in tissues) discharge their granules releaseing heparin and histamine to reduce blood viscosity and encourage vaso dilation. This increases blood flow and therefore flow of leucocytes to the area of infection (inflammatory response). Mast Cell activation also attracts Eosinophils which combat parasitic worms {if present) and neutralise/control inflammatory response Immature B cell created from Stem Cell in Bone Marrow (displays IgM on surface) _—_____¥ Immature B cell leaves bone marrow and circulates through blood and lymphoid tissue. As it leaves bone marrow it begins displaying IgD as well as IgM on surface. Now a Naive (aka Virgin) B Cell Naive B cell in primary follicles of lymph nodes endocytoses and presents unbound cognate antigen & becomes activated with a 2nd signal from conjugate Tht cell. Beells that don't bind to antigen die in 1 week Fe Th-Cell (T-helper) binds with MHC Il ‘on APC and upregulates expression of CD40L (activation). CD40L binds with CD40 on APC leading to greater expression of MHC (verification) and greater activation Activated B cells travel to dark zone of germinal centres in 2ary follicles, express less Ig and undergo Clonal Expansion (proliferation) and somatic hypermutation (Expression of varying affinity 1g) Now known as Centroblasts = ‘APC (macrophage, neutrophil or dendritic cell) displays antigen. APC. displays using MHC Class-I or Class-II molecule. Others only present using MHC Il APC travels to lymph node T-cells produced in bone marrow and travel to thymus for maturation T-Cells which can'tbind to MHC, fail to bind to MHC or have an over affinity for MHC and self-antigen undergo negative selection. Those that can bind with self-MHC survive and specialise into those that can bind with Class | (CD8 Cytotoxic T-Cells) and Class II MHC (CD4 Helper T-Cells) Te Cell (Cytotoxic / CTK Cell) binds) with MHC | on Dendritic Cell and upregulates expression of CD40L (activation). CD40L binds with CD40 ‘on APC leading to greater expression of MHC | (verification) and greater activation of Te-Cell (Overall = co-stimulation). of Th-Cell During proliferation B-cells can also switch (Overall = co-stimulation) classes if stimulated by a cytokine by v changing the constant region of their immunoglobulin e.g. IgM to IgG or IgA. This allows the Fc part of their antibodies to bind with different receptors and perform different Once activation is complete, cells disengage and Th cell proliferates ¥ Onee activation is complete, cells, disengage and Te cell proliferates. functions, Vv pT Centroblasts proceed to Basal Light zone and become Centrocytes, Here they are exposed to antigen presented by FDCs. Those with low affinity to antigen are destroyed FH Surviving Centrocytes progress to Apical light zone and present an antigen on MHCII to Th Cells. Those that are recognised receive Ja“ signal to differentiate into Memory cells (detector) or Plasma cells (Antibody factory) After many generations, Th-cells mature into Effector, Memory (effector cells for future infections) and Regulator (prevents over-active immune response) Effector Th Cells co-ordinate immune response by stiumlating response of 4 — other cells including B-Cells (Th1) and Macrophages (In Innate System) (Th2) and Tc Cells (Th2) (a ¥ Te calls leave lymph node and travels to area of infection. Intracellular infection occurs Infected cell displays fragments of virus on surface using MHC Class-| molecules Te cell identifies infected cell Infected cell activates Tc Cell (prevents killing of healthy cells) KEY Macrophage’ Tell ‘Antibodies secreted by plasma cell bind with Te-Cell destroys infected cells by apoptosis Phagocyte digests remains of pathogen antigen and opzonise pathogen or can pectic neutralise viruses aE th Cell jatural Killer — Phagocyte engulfs pathogen )) 
