Zoology 101: Animal Biology Last Lecture Outline Lecture 29 1. Stress and the body's response1. hormones 2. Immune systemCurrent lecture 1. Lymphatic system2. Adaptive immunityLymphatic system• Phagocytes and other leukocytes• overlays capillaries (can travel in lymphatic system or circulatory system)• Phagocytic cells are nonspecific defense ◦ phagocytosis: ingestion of invading organisms by specific leukocytes ◦ neutrophill: 60-70% leukocytes, self destruct with pathogen, short lived ◦ macrophages: 5% are leukocytes, 'big eaters', long lived, large • Phagocytes engulf pathogens- form a vacuole that fuses with a lysosome ◦ microbes ingested (endocytosis) ◦ microbe vacuole fuses with lysosome ◦ enzymes destroy microbes and and leaves cell via exocytosis • Inflammation is a nonspecific response to infection or injury◦ Injury → mast cell release histamine → dilates capillaries and makes them leak → cytokines (chemicals that synchronize immune function) attract phagocytesAdaptive immunity • Develops after exposed to a foreign body • Relies on lymphocyte (white blood cells) (type of leukocytes → specific defense) ◦ T cells: lymphocyte that matures in thymus ◦ B cells: lymphocyte that matures in bone marrow◦ both originate in bone marrow • Humoral response◦ B cells; anitbodies defend against infected body fluids • Cell mediated response: T cell- cytotoxic cell defend against infection in body cell • Antigen: substances that elicit B/T cell response ◦ contains small, accessible parts (epitope)◦ Antigen receptor binds with epitope → response (either cytotoxic T cell or helper T cell)◦ Each individual lymphocyte is specialized to recognize a specific type of molecule • Surface proteins with binding site (receptors) on B cells; can bind to pathogen via shape-specific site• B cells binds to pathogen, antibodies are produced by B cells and important for marking pathogens for destruction • Antigen receptor specificity ◦ Antibodies can recognize distinct epitopes on same antigen or free antigens • Antigen recognition by T cells ◦ Similar as B cell, but functional response is different ◦ T cells bind to antigen fragment- displayed by MHC molecules ◦ MHC- major histocompatability complex • Class 1:◦ Interacts with cytotoxic T cell▪ an antigen fragment in the cell associates with an MHC molecule and transported to surface ▪ combination of MHC and antigen is recognized by T cell, alerting it to the infection ▪ Activated cytotoxic T cells kills infected cell 1. Cytotoxic T cell binds to class 1 MHC antigen fragment2. Activated T cell releases perforin → forms pores in membrane of infected cell3. Infected cell fragments and dies, cytotoxic T cell is released • Class 2: Helper T cells ◦ Transports fragments to cell surface ◦ MHC molecule and antigen recognized by T cell ◦ Helper T cell all trigger humoral and cell mediated immune response ◦ Helper T sends signals to: ▪ B cells to initiate production of antibodies ▪ Cytotoxic cells to initiate destruction of infected cells • Activation of B cell in humoral immune response ◦ activation of helper T cell occurs after recognition of an antigen fragment displayed by class 2 MHC molecule ◦ B cell displaying same antigen fragment and class 2 molecule bind to activate helper t cell◦ activated B cell proliferate and differentiate into memory B cells and antibody-secreting plasma
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