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Adaptive Immunity: Lecture 5 (Info on dependent response (most…
Adaptive Immunity: Lecture 5
T dependent antibody response
When an antibody response depends on interaction with helper T cells
independent: responses that act against molecules with multiple repeating epitodes
followed by endocytosis and processing of the antigen
the dendritic cell presents epitopes in conjunction with its MHC II proteins
the APC will induce the specific T lymphocytes with the TCR complimentary to MHC H-epitope complex
the activated Th 2 cell must in turn induce the specific B cell that recognizes the same antigen
lymph nodes will facilitate and cytokines mediate interactions among the antigen cells and lymphocytes
will increase the chance that the correct cells find each other
dependent response: begins with actions from the antigen presenting dendritic cell (APC)
Steps for Dependent Response
Step 1. Antigen presentation for Th
after the dendritic cell acquires antigens in the skin or mucous membrane it moves by lymph to the local lymph node
helper T cells pass through lymph node and survey all the resident APC's for the compliment epitopes in conjunction with MHC II proteins
once they've established immunological synapse CD4 molecules in the membrane rafts of the Th cells cytoplasmic membrane recognize and bind to MHC II; causes stabilization of synapse
Helper T cells need a second signal by displaying an integral membrane protein in the synapse; this induces Th cells to produce clones
Step 2. Helper T cells into Th cells
the cytokine interleukin 4 (IL-4) acts as a signal to the Th cells to become type 2 helper T cells
immunologists think the IL-4 comes from being secreted by innate cells or later by response of Th cells themselves
Step 3. Activation of B cells
B cells and newly formed Th cells survey one another
a Th cell binds to B cell with an MHC II protein-epitope complex that compliments the TCR of the Th2 cell
CD4 glycoprotein again stabilizes immunological synapse
Th2 cells secrete IL-4 that induces selected B cell to move to the cortex of the lymph node
a th2 cell in contact with an MHC II protein-epitope on the B cell is stimulated, expresses a new gene products, and inserts a protein called CD40L into the cytoplasmic membrane
CD40L binds to CD40, found on B cells
provides a second signal in immunological synapse and triggers B cell activation
these processes are called clonal selection b/c they pick a specific B cell
Step 4. Proliferation/ Differentiation of B cells
the then selected b cell proliferates rapidly to produce a population of cells (clones) that make up a primary follicle in lymph node
clones then differentiate into two types of cells: memory B cells or antibody-secreting plasma cells
Info on dependent response
most differentiated B cells become plasma cells
the plasma cell descendents of single activated B cells secrete antibodies with binding sits identical to one another and complimentary to specific antigen recognized by the parent cell
plasma clones will replicate and their antibodies will slightly differ in variable regions
they secrete more survival advantaged antibodies to fight epitopes
each plasma cell produces different classes of antobodies
Begin with secreting IgM then switch to other like IgA, IgE, or IgG
controlled by Th cells and is irreversible
secrete own body weight in IgG a day
individual plasma cells don't live that long b/c of metabolic rate
they usually die in a few days of activation
antibodies can remain for a few weeks and the descendents live on for years to be in adaptive immunity
Memory Cells and Immunological Memory
some cells survive as memory B cells
they are long-lived cells with a BCR complimenting their specific epitope that triggers production
they retain their BCR's and persist to lymphoid tissues to possibly survive 20 years.
they initiate antibody production if same epitope come back
Tetanus Example
the body produces few Th cells and B cells bind to and respond to epitopes of tetanus toxoid: a deactivated tetanus toxin used in immunization
primary response
small amounts of antibodies produce and take days before a sufficient antibody amount is made to eliminate all the toxoid from the body
some may persist for weeks(3) and ends when plasma cells live out normal life
memory B and T cells in the lymphoid tissue gives resources of antigen-sensitive cells to become active when exposed to antigen
in tetanus case it's the tetanus bacteria; exposure can occur years later
tetanus toxin produced during infection stimulates memory cells population
proliferates and differ into plasma cells with activation by APC
new plasma cells produce increased amounts of antibodies within days so disease is neutralized before it starts anything
Secondary immune response
memory cells recognize and respond to antigen and is a type that is faster and more affective than primary
Third response
results in an even more effective response
the immune response is more enhanced and triggered by the following exposure to antigens
this response is based on memory
this type is the basis for immunization