Adaptive Immunity When innate immunity isn t enough to clear an infection adaptive immunity can assist Characteristics Found in higher vertebrates High degree of specificity o Immune receptors and antigens T cells possess T Cell Receptors TCRs Recognize intracellular pathogens e g viruses B cells possess B Cell Receptors BCRs Also known as immunoglobulin receptors Recognizes extracellular antigens e g in the bloodstream o The smallest part of an antigen that can be recognized is an epitope Epitope the specific place on the antigen that the T or B cell binds to Each antigen may have multiple different epitopes each capable of being recognized by a different B or T cell and stimulating a response Tolerance of self o Includes tolerance of bacteria that are part of self o B cells originate and mature1 in the bone marrow o T cells originate in the bone marrow and migrate to the thymus for maturation o Lymphocytes and lymphoid tissues Once mature lymphocytes are expelled into the bloodstream as mature na ve lymphocytes Migrate through secondary lymphoid tissues throughout the body Tonsils spleen Peyer s patches lymph nodes lymph vessels appendix Diversity Memory o All TCRs BCRs are unique except for clonal copies o During development gene rearrangements and sloppy construction occurs on purpose to produce a very large number of unique BCRs and TCRs This increases the chances of a reaction against pathogens o Receptors are formed before exposure to pathogens occurs o Exposure to a new infectious agent produces a primary immune response Takes about 7 14 days to peak Clear pathogens and produces memory lymphocytes o Subsequent exposure results in a secondary anamnestic immune response Faster and more potent than primary immune response Divisions of Adaptive Immunity 1 Humoral immunity a Regulates pathogens outside of cells extracellular 1 Maturation is where immune cells are taught what self looks like and develop their TCR BCR to detect foreign molecules They are screened to see if they react to self If T cells react to self they are destroyed good T cells do not react to self cells they are sent into the peripheral bloodstream If B cells react to self they become inergic cannot be stimulated good B cells are released and go to secondary lymphoid tissues b B cells i Made and mature in bone marrow then good B cells are released and go to secondary lymphoid tiisues to wait for a recognizable antigen to pass by If a recognized antigen comes by the B cell becomes activated ii 1 The B cell phagocytizes the entire pathogen including its antigen a This partially activates the cell b Rarely an antigen may be able to completely activate a B cell 2 Helper T cells come along to complete activation iii B cells bind to extracellular antigens on their own so long as they have the specific 1 Receptors have a cytoplasmic tail to relay the information from outside the a TH2 cell receptor cell to inside iv An activated B cell will make identical copies of itself clonal activation 1 They will have the same B cell receptor 2 Clonal cells differentiate into a Effector cells aka plasma cells i Secrete antibodies ii Antibodies are exact copies of the receptor they will all specifically recognize that same receptor 1 Antibodies can be used to neutralize a toxin 2 Antibodies do not kill just bind 2 Cellular immunity a Responds to intracellular problems b Memory cells i Pathogens e g viruses ii Anything going wrong inside the cell e g cancer and tumors b T cells i Divas Only recognize antigens when another cell and antigen presenting cell dendritic cell macrophage or B cell processes and presents it to them ii Each TCR consists of two different polypeptide chains alpha and beta 1 The tips of each chain constitute the variable region a Here and ONLY here is where gene splicing is sloppy to allow for diversity 2 The bottoms constitute the constant region iii Activation of T Cells 1 Requires the binding of the TCR with the specific peptide presented on the major histocompatibility complex molecules of APCs 2 Co receptors CD 4 or CD 8 must correctly interact with the MHC molecule a CD4 Helper T cells interact with MHC class II b CD8 cytotoxic T cells interact with MHC class I 3 Activated T cells expand and differentiate into either effector cells or memory cells a Effector T cells i Action cells ii Short lived iii Armed with direct immune functions iv Effector form depends on co receptors 1 CD4 Helper T cells secretion of large amounts of cytokine to enhance and direct actions of other immune cells 2 CD8 Cytotoxic T cells cytotoxic killing of infected cells by release of granzymes perforin near contacted target cells initiating apoptosis b Memory T cells i A late encounter occurs between a memory T cell and an APC presenting the same antigen activation and clonal expansion occur again creating more effector cells and memory cells iv Helper T cells 1 CD4 2 Central to the immune system major communication molecule 3 Releases molecules cytokines to call in innate immune system cytotoxic T cells or activate B Cells a TH1 cells activate cytotoxic T cells IL 2 Interleukin 2 proliferates CD8 T cells IFN gamma Interferon gamma anti viral i ii iii TNF alpha Tumor necrosis factor induces apoptosis of cells b TH2 cells activate B cells IL 4 IL 5 i ii Proliferation of B cells iii Differentiation of B cells into plasma cells and secretion of v Killer T cells antibodies 1 Essentially NK cells with a receptor 2 Destroy cells specifically 3 Activated specifically by TH1 cells 4 Activation of CD8 T cells produces effector killer T cells and memory killer T cells a Killer cells recognize targets by their presentation of antigen epitope fragments on MHC class I b Killing is achieved by T cell release of perforin granzyme inducing apoptosis in the target 5 Recognition and killing of target cell by an effector cytotoxic T cell a T cell binds to the infected target cell causing degranulation b Target cell undergoes apoptosis Antigen Processing Exogenous antigens and the endocytic pathway o Broken down and presented on MHC II molecules This restricts presentation to CD4 T cell which can bind to MHC II structures o Once presented initiates activation of Helper T cells Produces effector cells secrete large amounts of cytokines and memory cells for later response o Steps 1 Antigen presentation and binding by CD4 T cells occurs 2 Activated CD4 T cell secretes IL 2 and expresses its receptor IL 2R for 3 Clonal expansion and differentiation