3/17/08 Lymphatic System Chapter 20 – Day 3

3/17/08 Immune Response  Definition of Immunity  Lines of defense – non-specific vs. specific  Characteristics & Function of non-specific  Mechanical & Chemical barrier & special cells  Phagocytes – chemotaxins, cytokines  NK cells – antigen recognition, perforin release  Interferons – anti-viral  Complement – help macrophages, attach opsonins  Pyrogens – raise temperature to inhibit growth  Inflammation chemicals

3/17/08 Specific Immunity  Recognize antigens, release antibodies  B-cells, T-cells (types)  Cellular vs. humoral  MHC-I picks up antigen + CD8 of cytotoxic T-cell  Antigen presenting cells, MHC II + CD4 helper T-cell, B-cell activation

3/17/08 Specific Immunity  Recognizes, responds & remembers specific substances (antigen-antibody recognition)  Cells involved: B-cells & T-cells  Different responses for different types of substances ♦Cellular Immunity Fungi, pollen, parasites, tumor cells T-cells destroy foreign objects ♦Humoral immunity Viral & bacterial infections B-cells are recruited There is antibody production = ANTIBODY MEDIATED  T-cells & B-cells are always circulating in the lymph  At the time of “invasion” they have to be activated to produce the immune response needed

3/17/08 Lymphatic System Fig

3/17/08 Activation Process  Every cell in the body (except RBC) contains a special protein ♦MAJOR HISTOCOMPATIBILITY COMPLEX – CLASS I ♦= MHC – I  Under normal conditions…  An infected cell… ♦An antigen from the “invader” binds to MHC – I = “red alert!” ♦The bound antigen attracts special/specific T-cell Cytotoxic T-cell CD8 protein ♦Sensitized Tc cell = activated ♦It now produces more Tc cells & Memory Tc cells (reserved for later) ♦Tc cells attach to invading cells & lyse them

3/17/08 Activation Process Fig

3/17/08 Activation Process – MHC II  MHC-II present on special cells ♦antigen presenting cells (APCs) & lymphocytes ♦Responsible for activating T-cell defenses against foreign cells (including bacteria) and foreign proteins ♦Phagocytic cells such as macrophages & microglia  Normal APC…  The APC will bind to the helper T-cell with CD4 marker  Helper T-cell is activated – releases cytokines to attract other cells  Memory T H cell is generated  Activate B-cells for antibody production

3/17/08 Activation Process Fig

3/17/08 Lymphatic System Fig

3/17/08 Antibody Mediated Immunity  B-cells must be activated  Requires ♦Antigen presentation on MHC II ♦Special cells: neuroglia, phagocytes, lymphocytes (B-cells) Are ANTIGEN PRODUCING CELLS (APCs)  Only APC have MHC II – distributed all over  If APC is attacked by pathogen, antigens brought in by the pathogen are displayed on MHCII

3/17/08 Recognition of Antigen  Helper T-cells have CD4  CD4 binds to antigen on MHC II  T H cells are activated by infected cells  Memory T H cells are produced  B-cells also present antigen on MHC II  Active helper T-cells with CD8 bind to B-cells  B-cells are activated  Cytokines released by helper T-cells also help in sensitizing  Active B-cells produce plasma cells  Plasma cells produce antibodies in massive quantities

3/17/08 Lymphatic System Fig

3/17/08 Antibodies  Antibodies are special proteins that…  Cause agglutination  Neutralize toxins  Increase non-specific defenses  Prevent attachment of pathogen cells  Controls infection  Levels of antibodies in the blood = titer  In a 1 st infection – you have a primary response ♦Antibodies take time to build up  Second infection = secondary response ♦Memory B-cells = immediate response ♦High titer gives resistance

3/17/08 Disorders of the Immune system  Autoimmune disorders ♦Attacks normal cells ♦Immune system makes antibodies against itself = autoantibodies ♦Normally: self-antigen recognition prevents attack  Examples ♦Multiple Sclerosis Immune system destroys the myelin sheath ♦Rheumatoid arthritis Attacks joints Autoantibodies accumulate in connective tissue

3/17/08 Disorders of the Immune system  Immunodeficiency disorders ♦Immune system functions abnormally  Example ♦“bubble boy disease” ♦SCID – severe combined immunodeficiency disease ♦It is a developmental problem – normal B cell production, but T-cells are affected ♦Can be caused by a viral infection ♦Acquired Immunodeficiency syndrome is caused by the human immunodeficiency virus (AIDS is caused by HIV)

3/17/08 Disorders of the Immune system  Allergies ♦Accelerated immune response ♦Excessive or inappropriate response such as inflammation  Lymph node blockage ♦Lymphatic filariasis (elephantiasis) ♦Caused by parasitic worms ♦Grossly swollen legs and arms

3/17/08 Lymphatic System Fig. 20.5

3/17/08 Lymphatic System Fig. 20.5