2 Flashcards
Explain the first line of defence and second line of defence
First line involves antigen uptake and processing by APCS and tcell activation producing cytotoxic T cells, also antibodies circulate
Second line involved bcell activation by T cells and plasma cell formation to produce antibodies
What are the major APCS in the storms of organs
Macrophages
What are the major APCS of epithelia
Dendritic cells
How does interstitial fluid enter the lymphatics- describe the vessels
Via collecting lymph vessels, have valves and sparse smooth muscles
What are the two drivers of lymphatic fluid
Smooth muscles rhythmically contracting and move my of tissue during eg exercise
From the lymph nodes what does the lymphatic fluid travel in
Larger collecting vessels with spirally arranged smooth muscle
Trucks
Subclavian veins
What is the structure of the epithelium of initial lymphatics
Cells are oak leaf shaped held together by adhesive junctions that leave the lobes frees moving
Flaps only allow moment in not out
What is the job of the secondary lymphoid organs
Filter lymph for antigen and allow matches before lymphocytes and APCS
What is a follicle made up of
Germinal centre and mantle zone
In a lymph node what is the first step
Activated macrophage or dendritic cell travel to lymph node and present protein fragments
What is the second step in the lymph node
B cells have picked up the antigen in the follicle infested and move to the b/t cell interface
Antigen presentation in the para cortex leads to T cell activation and proliferation
What is the third step in lymph nodes
T and b class specific for this antigen meet at the b/t cell zone interface and the t helped cell activates the B cell to proliferate and mature
Where are the follicular dendritic cells and what is their job
B cell follicles
Long extensions that form networks, they bind the antigen in native form conformation and present it on their surface for a long time
How can an antigen get into the lymph node
A) opsonised by antibody or complement
B) as a small soluble or proteolyzed antic
C) carried by a APC ( dc)
If a B cell doesn’t find a match in the follicle what else can it do
Help ferry antigen to FDC’s
What is the supporting network or a lymph node made from
Strong trabecular of lymph node and Reticular fibres from reticular cells
What are reticular fibres composed of
Collagen 111 and 1
What is the free space been the wrapped reticular fibres
Transport venue- conduit for small antigens
What is the first step in B cell activation
Either internalise a soluble native antigen or form an immunological synapse with a T cell, if the fitting antigen is part of a larger complex bound to a APC or FDC’s
Antigen attached to the B cell receptor is internalised and transferring a lysosome where it is loaded onto MHC11 ( has come from ER with protective cap- invariant chain- cleaved off in lysosome before loading)
What is the second step in B cell activation
Antigen attached to MHC is presented to the T cell at the b/t cell interface
What happens if the B cell finds it T cell match
T helper cell activates the B cell to proliferate into
IgM producing plasmablasts
Remaining B cells move to germinal centre for maturation
What is the key enzyme generated the mutations and how
Activation induced deaminase
Point mutations in the variable region of the B cell receptor, cleaved off NH2 groups of some cytosines- making it uracil
Uracil is rna equivalent of DNA thymine. In next round of replication, uracil read as thymine, means base pair CG changed to AT
Why must the B cell undergo hyper mutation and elimination
Because B cell clone receptor binding to antigen is specific but not super tight, need to select clone with high affinity
What at the steps of hyper uracil and elimination
T/b cell interaction at border and receiving of co-stimulators signals
Selected cells enter dark zone of Gc
Undergo somatic hypermuation ( upregulate component of shm machinery and activation of aid)
After 1 or more calves B cells move to light zone
BCRs exposed to antigen by FDC’s
Low affinity ones undergo apoptosis
High affinity ones compete for T cell help
The survivors have three routes
