Defense mechanism against pathogens
Defense mechanism against pathogens
Immune SystemWhat is immune system?
Cells and organs within an animal’s body that contribute to immune defenses against pathogens (병원체)
Bacteria -Major entry points ;open wounds, inhalation, and ingestion
Parasites -Fungi, worms -Damage host by using host nutrients or secreting toxic chemicals
Viruses -May kill host cell rapidly or lie dormant for a period -May cause cancer
The job of the immune system is to 1) keep pathogens out and
2) keep pathogens if they enter the body
Immune SystemTypes of Immune system
1) Innate immune system (non-specific)
2) Adaptive immune system
Immune SystemTypes of Immune system
1) Innate immune system (non-specific)
Defense system present at birth
Protect against foreign cells or matters regardless what they are
Doesn’t require prior exposure to invaders
Innate Immune System
• First line of defense
=> If the first line of defense fails
• Second line of defense
Keep pathogens out
Players: •skin (protects body against several pathogens •stomach acid (kill pathogens including bacteria)
•mucus: trap pathogens
Kill pathogens
Players: • Phagocytes
Innate Immune System
• Second line of defense
Kill pathogens
Phagocytes : cells capable of phagocytosis (engulfing particulate matter and destroy = Eat it up)
- Present in all classes of animals- Most fundamental and ancestral of body defenses- In vertebrates, most are leukocytes (WBC) e.g., neutrophils, macrophages, natural killer (NK) cells, Basophils, - Dendritic cells
- Mast cells
Innate Immune System
• Second line of defense
Kill pathogens
Cells involved in the innate immune system
Innate Immune System
Innate Immune System
Bacterium
phagosome
Lysosome
The bacterium (upper right) is engulfed in a section of the cell's membrane
Form a structure called a phagosome
Fuse with lysosomes
Digestive enzymes in lysosomesdestroy bacterium
Innate Immune System
• Second line of defense
Kill pathogens
Phagocytes : cells capable of phagocytosis (engulfing particulate matter and destroy = Eat it up)
- Present in all classes of animals- Most fundamental and ancestral of body defenses- In vertebrates, most are leukocytes (WBC) e.g., neutrophils, macrophages, natural killer (NK) cells, Basophils, - Dendritic cells
- Mast cells
Can recognize general features of cancer or virus-infected cells and kill them
Innate Immune System
Innate Immune System
• Second line of defense
Inflammation
Small injuries e.g., cuts
- Symptoms: redness, swells, pus, heat
Why do these symptoms occur? Inflammatory response
- Innate local response to infection or injury
- Destroys or inactivates foreign invaders, clears infected area of dead cells and sets stage for tissue repair
Innate Immune SystemInflammation
Injury introduce bacteria⇒Mast cells secrete
Histamine and endothilial cells secrete nitric oxide=> Dilation of vessel
Capillaries dilate and become Leaky
⇒Fluid and leukocytes enter the site of wound
neutrophil
Neutrophils and otherphagocytes engulf and destroy bacteria
=> Capillaries return to normal
Innate Immune SystemInflammation
Innate Immune System
Other types of innate immune system
Players : Antimicrobial proteins (proteins involved in killing microbes 미생물)Interferon
Secreted by most cellsInhibits viral replication inside host cellsNot specific to a particular virus
ComplementKills microbes without phagocytosisUses membrane attack complex (MAC) to create channels in microbial plasma
membrane (=poke holes in the membrane of microbes)Causes microbe to burst
Innate Immune System
Complement
Immune System
Innate immune system (non-specific)
•Defense system present at birth
•Protect against foreign cells or mattersregardless what they are
•Doesn’t require prior exposure to invaders
Acquired immune system (specific)
•Involves antigen (항원) :any molecule thatthe host doesn’t recognize as itself
•Requires exposure to foreign substances
Aquired Immune System
•Players
Lymphocytes (림프구): •Type of white cells
•Required for the acquired immune system
Cytotoxic T cells :directly kill target
Helper T cells :Assist in activating BCells and cytotoxic T cells
Aquired Immune System
3 stages of response1)Antigen encounter and recognition by lymphocytes
2) Lymphocyte activation and cell division to produce effector cell andmemory cells
3) Attack launched by activated lymphocytes and/or their secretions
Aquired Immune System3 stages of response
1) Antigenencounterand recognitionby lymphocytes
•During its development, each lymphocyte synthesizes a membranereceptor that can bind to a specific antigen
•Antigens that bind to a lymphocyte receptor are recognized by thelymphocyte
•Each lymphocyte is specific for just one type of antigen
Antigen
Aquired Immune System3 stages of response
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
Antigen
•Upon binding the antigen, lymphocyte undergoes cell division•progeny all express the same receptor :clonal selection•B cells proliferate into plasma cells that make antibodies (each B cell can secreteonly one particular type of antibody (항체)
Aquired Immune System3 stages of response
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
3) Attack againstspecific antigen
Antigen
Effector cells carry out the attackMemory cells that remain poised for future attacks
Secrete antibody that bind to antigen(humoral immunity)
Directly attack antigen bearing cells(cell-mediated immunity)
Aquired Immune System3 stages of response
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
3) Attack againstspecific antigen
Antigen
Later, plasma cells and cytotoxic T cells die to prevent excessive immune response
Memory cells persist, waiting future attacks
Humoral Immunity (체액면역)B cells and Humoral immunity
Humoral Immunity (체액면역)Antibody
Constantregion
Variableregion
Immunoglobulin protein familyEach composed of 4 interlinked polypeptides
2 long heavy chains2 short light chains
Constant region : identical for all antibodies of a given class Variable region : antigen binding site, each ab has different variable region => bind to different antigen
Humoral Immunity (체액면역)B cells do not attack pathogens directly. Instead, secrete antibody( Ab)
Ab can in activate pathogens by
1) Physically link the pathogens to phagocytes, complement proteins and NK cells
2) Ab directly binds to toxin of pathogen: inhibit the function of toxin
Aquired Immune System3 stages of response
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
3) Attack againstspecific antigen
Antigen
Pathogen present
Antigens such as proteins from pathogens are broken downin endosome
Fragments of antigen (epitope)are complexed with MHCII
Transported to plasma membrane
Epitope-MHC complex is recognizedby T cell receptor
T-cell activation e.g., cytokine secretion : IL2 => promote division of helper
T cells
Helper T- Cell activationAntigen presenting cells
Phagocytosis by macrophage orNK cells
Pathogen
Helper T-cell receptor
cytokine secretion : IL2
B Cell activation by activated T-cells
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
3) Attack againstspecific antigen
Antigen
Memory cells persist, waiting future attacks
Activated helper Tcell
Bind to B-cellpresenting sameantigen=> promoteclonal selection
B Cell activation by activated T-cells
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
3) Attack againstspecific antigen
Antigen
humoral immunity
Summary of events in a humoral immune response
Summary of events in a humoral immune responseMost of eventhappen within alymph node
Bacteriaenterthe body
Bacteria are carriedinto lymph nodeand phagocytosisby macrophageoccurs
phagocytosis by B cells and B cell present Ag
1
2
Macrophagepresent Ag toa helper Tcells andsecret IL1
helper T cell isactivated-> secret IL2and othercytokines->Division
Activated Helper Tcellbind to B celldisplaying the sameantigen
Activation of B cells
Some B cells-> plasma cells
Other B cells-> Memory B cells
Antibody secretionby B cells->destroy bacteria
Cell mediated immunity
1) Antigenencounterand recognitionby lymphocytes
2) Lymphocyte activation and cell division
3) Attack againstspecific antigen
Antigen
Memory cells persist, waiting future attacks
Cell mediated immunityCytotoxic Tcell binds to thesurface of virusinfected cells
Cytotoxic T cellsbind to othervirus-infected cells
Helper T cell activation(same mechanism as inhumoral immune response)-> promote proliferastion andthe activation of Cytotoxic Tcells
Cytotoxic T cells secrete perforin-> inserted into the plasma membrane ofvirus-infected cells -> Cells burst
Some cytotoxic T cells do not complete full activation and remain as memory cells
Cell mediated immunity
Immune memory
Primary immune response•Initial exposure to an antigen•Antibody productionis slower andlower
Secondary immune response•Subsequent exposure to same antigen•Faster and larger antibody production•Memory B cells quickly stimulated to differentiate and multiply•Immunological memory