5 Outline Anatomy of the Immune system Organization of the body’s defensesHumoral immunityCell-mediated immunityImmune responses in Health and diseases
6 Organization of the body’s defenses Non-specific defenses: no need to decipher pathogen’s identiy. Always present in the body.- Physical barriers- Inflammation- Interferons- Natural cell killers (NK cells)- Complement systemSpecific defenses:Based onn recognition of the pathogen’s identityHumoral immunityCell-mediated immunity
7 Non-specific defenses Physical barriers- skin- mucus- stream of tears or urine- InflammationChemical barrierspH (stomach, vagina)enzymes (stomach, tears)InterferonsComplement system
8 InflammationSymptoms of inflammation:RednessheatSwelling- pain
11 Interferon Protein secreted by a cell currently infected by a virus Interferon warns the neighboring cells of the impending viral infectionThe neighboring cells synthesize proteins that will block the virus from hijacking the cell DNA replication machineryAnimation:
12 Complement system About 30 blood proteins They become activated either by direct contact with a pathogen or by contact with a bound antibody.In an activated state, they form a complex which opens a hole in a pathogen’s cell membrane bacterial lysisComplement system also promotes inflammation
13 Natural Killer cells = NK cells Cytotoxic T cells, lacking markersAble to recognize a wide range of pathogens without prior exposureWhen recognition and binding occur, the NK cells destroy the pathogen through cell lysis
14 Specific immunitySpecificity: based on shape recognition of cell surface antigensDiversity: Any shape can be recognized by a B or T-lymphocytes and trigger an immune reactionMemory: once a pathogen has activated the immune system, memory cells remain and will protect against a secondary infectionSelf-tolerance: the immune system does not attack itself
15 Specific immunity = the players Macrophages (antigen presenting cell = APC): phagocytize pathogens and present antigens to helper-T lymphocytesHelper-T lymphocytes: secrete lymphokines and activate B and killer T lymphocytesB-lymphocytes: multiply and specialize into plasma cells secrete antibodiesKiller-T lymphocytes: kill (through lysis) infected or cancerous cells
16 Outline Anatomy of the Immune system Organization of the body’s defensesHumoral immunityCell-mediated immunityImmune responses in Health and diseases
17 Antibody-mediated (humoral) immunity = AMI 1- Macrophages phagocytize a pathogen and present an antigen to a matching helper-T cell2- At the same time, some pathogens contact B-cells matching the pathogen’s antigensThe helper-T cells multiply, secrete lymphokines which stimulate the B-cells to multiply and specialize into plasma cellsThe plasma cells secretes antibodies
19 What are antibodies? Structures formed by 4 proteins Two main regions: the upper region is highly variable and bind to a specific shape (the antigen)The base region is constant for all antibodies this region, when the antibody is bound to its antigen, activates the complement system
21 Types of antibodies Antibody = immunoglobulin = Ig IgG Most abundant. mostly in blood, lymph. able to cross the placentaIgA Found in tears, milk, blood, lymphIgM First antibody to be secreted. found in blood, lymph. unable tocross placentaIgD Found in blood, lymph, on B cellsIgE Found on mast cells, basophils. involved in allergic reaction.
23 Clonal selectionOnce a T, B or killer lymphocytes have made contact with their specific antigen, they are triggered into action but they also divide and form a large amount of identical cells, called a clone.
24 Clonal deletionHow can the DNA in the nucleus codes for each type of antibody?Since over a millions of different types are needed, how can the DNA in the nucleus code for each of them? There is clearly not enough DNA to accomplish that.During embryogenesis, several genes coding for the variable portion of the antibody (and each responsible for part of a shape) reshuffle so each combination of genes codes for a specific antibody (and shape). So a stem cell receives the capability to form one single type of antibody.Once formed, they circulate in the body. If they meet and bind to a shape (formed by a protein) present in the body, they are destroyed or deleted, so that only the stem cells responsible for antibodies aimed at foreign pathogens are left.A stem cell able to react with our own proteins and not deleted during fetal life might later trigger an autoimmune disease.
25 Outline Anatomy of the Immune system Organization of the body’s defensesHumoral immunityCell-mediated immunityImmune responses in Health and diseases
26 Cell-mediated immunity Similar reaction to AMIThe pathogen triggering the reaction is a virus infected cell or a cancerous cell.Killer T lymphocytes are sensitized by contact and activated by lymphokines secreted by activated helper T lymphocytes