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10 Cards in this Set

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  • Back
Define extracellular bacteria infections
-They are infections where bacteria can live outside cells after entering the body
-That is bacteria do not invade and live inside the cells of the host
Let's say that you cut your finger on a dirty nail that is covered with bacteria. How do we deal with this type of infection?
-Body would first mount an innate immune response to try to eliminate the bacteria
-In most cases the innate immune response eliminates the infection
-However, if there are large numbers of bacteria, it could overwhelm the local non specific defenses
-Bacteria will divide and spread and the adaptive immune system is activated as a last line of defense. For this type of infection the production of antibodies would be the most appropriate form of an adaptive immune response
After the skin has been punctured and bacteria have entered the wound, the innate immune responses will be initiated. What follows next?
1) At site of tissue damage, mast cells that reside in tissues release substances (including histamine and tumor necrosis factor) that increase blood flow to the area
-Results in inflammation (redness, swelling, increased local temperature)
-Complement protein from blood enters tissues and complement proteins can kill many types of bacteria
2) Mast cells release substance that help recruit neutrophils and monocytes to the site of infection
-Neutrophils arrive at site of infection within minuntes and immediately begin ingesting bacteria( phagocytosis) after several hours monocytes that have entered the tissues differentiate into macrophages which are very efficient phagocytic cells and also secrete bactericidal substances
If innate immune response was not succesful in eliminating the bacteria the information that you have an infection in your finger is brought to the lymph node where there are large numbers of lymphocytes. What does this trigger?
The adaptive immune responses will be initiated
When the adaptive immune response is initiated what happens first to the extracellular bacteria?
bacteria that are present in the tissues can be picked up by the lymphatic system which drains all the tisuses of the body and they are carried to the local lymph node
In the adaptive immune response what happens first
Type of dendritic cell in the skin called Langerhans cell can engulf the bacteria and process (digest) the bacteria and display antigenic peptides on the MHC class II proteins
-Denderitic cell migrates from skin to nearby lymph node where it presents the antigenic peptide fragment to a T helper cell
-TCR of T helper cell binds to the MHC class II peptide complex and the CD3 complex sends a signal to the nuclues (signal 1 of T cell activation)
-CD28 molecule on the T cell interacts with the B7 co-stimulatory molecule on the dendritic cell (signal 2 of T cell activation)
-T helper cell receieves cytokines that instructs it to develop into a TH2 type T helper cell
-APCs produce different cytokines depending on whether the bacteria infection is intracellular or extracelluar.
-T helper cell will start to express CD40L on its cell surface
In the adaptive immune response what happens next
B cell express membrane bound immunoglobluins mIg
-Bacteria bind and cross-link the mIg protion of the BCR resulting in a signaling cascade intiate by Ig-alpha/Ig -beta co stimulatory molecules (signal 1 of B cell activation)
-Antigen is then processed inside an endosome and peptide fragments are displayed on MHC class II proteins
-B cell also increases its production of ribosomes and ER in prepartion for becoming an antibody factor
-Cuases the cell to get much larger and B cells will start to express B7 molecules on its surface
In the adaptive immune response what happens next
TCR of the Th2 cells bind to the MHC class II peptide complex on the B cell and the CD28 of the T cell binds to the B7 of the B cell
-CD40 molecule on the B cell binds to the CD40L of the TH2( signal 2 of B cell activation) and the Th2 cell provides the B cell with cytokines resulting in the complete activation of the B cell
-IL-4 secreted by activated Th2 cell causes the activated B cell to divdie
In the adaptive immune response what happens next
Activated Th2 cells and B cells divide many times, some B cells differentiate into memory cells (important for furture responses) and some differentiate into plasma cells
-Large increase in the number of T and B cells increases the size of the lymph nodes and results in swollen glands
In the adaptive immune response what happens next
After 5-7 days for a (primary response) plasma cells start making and secreting antibodies
-IgM antibodies secreted by plasma cells enter the blood and travel all over the body including the site of infection and anywhere else the bacteria have spread to.
-Antibodies will bind to the bactiera and neutralize the bacteria (prevent it from attaching to surfaces and activate complement to kill the bacteria)