Adaptive Immunity Study Notes

- involves a specific immune response to each particular microbe - it is able to adapt/adjust the response to each unique challenge - involves humoral / cell mediated immunity What is Adaptive Immunity - Phagocytise pathogens Role of Dendritic cells in Adaptive immu- - Antigen presenting cells (display their nity: antigen) = activates the T & B cells - MHC class restriction - Effector function What are T-cells subdivided based on ? - Dendritic cells recognise pathogens, engulf them by phagocytosis degrading them internally = forms phagolysosome - Antigens then bind to major histocompatibility complex protein (MHC) Cell mediated immunity (T cell) - De- Antigen MHC complex is released from scribe antigen presentation by dendritic the vesicle and travels to outer surface of cells ? dendritic cell membrane - dendritic cell membrane is now presenting antigen 'sampled' from the pathogen = this is used activate adaptive immune system (T cells) Dendritic cells and the Lymphatic system: - Immature dendritic cells resident in a tissue take up pathogens & their antigens by macropinocytosis + receptor mediated endocytosis - recognition of the presence of pathogens stimulates them to move through lymphatic system and reach lymph nodes: - arrive as fully mature non-phagocytic dendritic cells that express antigen - they activate naïve T cells that recognize the antigen = stimulating lymphocyte proliferation and differentiation. 1/5 T Cell Activation (Th1 response) - T cell activation by a dendritic cell requires 2 cell signals for the initiation of an immune response 1. Interaction between TCR-MHC/peptide: - TCR on the T Cell what are the 2 signals needed for Tc cell - MHC peptide on APC activation? 2. Co-stimulation by B7-CD28 - B7 expressed on APC - CD28 on the T Cell What is IL-2 ? Interleukin-2 (IL-2) receptor - it is a proinflammatory mediator (chemical mediator) Co-stimulation & Interleukins - Naïve (inactive) T Cells express low levels of the interleukin-2 (IL-2) receptors - Activation T Cells produce T-cell growth factor - Activated T Cells = increase expression of IL-2 receptor - IL-2 binds to high infinity receptor = sends signal to the T Cell IL-2 signal: - Induces T Cell proliferation - T cells numbers increase enabling an effective immune response Where do many bacteria that cause infectious diseases in humans multiply ? - The extracellular fluid = fluid that surrounds our cells How do intracellular pathogens move around in the body? - they use the extracellular space in the body to move from cell to cell through extracellular fluid - lymphatic system - Lymph nodes & spleen Humoral immune system: How are the extracellular spaces in the - Activated B cells (plasma B cells) = body protected ? produce antibodies - Antibodies bind to invading pathogens 2/5 = prevents spread of infection by killing the pathogen What are the 3 main professional types of APC's ? - Dendritic cells - Macrophages - B Cells Types of Antigen presenting cells : Role of Dendritic cells ? - Antigen presentation - activation of T Cell response Types of Antigen presenting cells: Role of Macrophages ? - Antigen presentation - Th1 killing of internalised bacteria Types of Antigen presenting cells: Role of B Cells ? - Present matched antigens to T Cells Where are all types of Antigen presenting cells (APC) found ? - Lymph nodes & spleen - B cells express specific receptors e.g., immunoglobins for soluble 'foreign' antigens - once they encounter antigen they enDescribe the antigen presentation of B gulf and express it cells ? - Antigen is internalised by Endocytosis - Antigen derived proteins (peptides) are selectively presented on the surface of the B cell by MHC Class II How many signals are required for B cell activation ? 2 signals : - Antigen signal - Activation from a T Cell B cell signals: Antigen signal (1) B Cell receptor and antigen B cell signals: Activation from a T Cell (2) CD40 ligand and cytokines What is linked recognition ? - Antigen presented by B Cell receptor must be recognised by a specific T Helper cell receptor - they must bear the same antigen What happens after both T&B cells have been exposed to the same antigen ? - cytokines are produced - B cell is transformed into an antibody-secreting plasma cell 3/5 - specific antibodies are produced to target foreign antigen' or infection. - Y-shaped Globular glycoproteins - also known as Immunoglobulins (Ig) - 2 heavy (identical) & 2 (identical) light polypeptide chains = held together by disulphide bonds Describe the structure of an antibody ? - can exist in 2 forms: secreted by plasma cells (white blood cells)/ expressed on the surface of B cells - shape of binding site is determined by order of amino acids in variable region - Brain = normally devoid of Immunoglobins - Epithelia = Dimeric IgA secretions across the epithelia Describe the distribution of antibodies in - Plasma = IgG & IgM is predominate the body ? here - Foetus = (IgG by transplacental transport) - Extracellular = IgG and monomeric IgA mostly found here. What type of antibodies are distributed in the Brain ? It is normally devoid of Ig What type of antibodies are distributed in the Epithelia ? - Dimeric IgA What type of antibodies are distributed in the Plasma ? - IgG - IgM What type of antibodies are distributed in the Foetus ? IgG - by transplacental transport What type of antibodies are distributed in the Extracellular fluid ? - IgG - monomeric IgA Antibody Function: Neutralisation - Antibody prevents bacterial adherence Antibody Function: Opsomisation - Antibody promotes phagocytosis 4/5 Antibody activates complement, which Antibody Function: Complement activaenhances opsonisation and lyses some tion bacteria. 5/5