2 Lymphoid organs Flashcards
primary lymphoid tissues
thymus and bone marrow
Most important in terms of releasing T and B cells that do not recognize self in strong way
Carry out function (no autoimmunity – release self-recognizing)
secondary lymphoid tissues
(many)
Sit waiting till pathogen comes along, they do circulate when waiting but housed predominantly in secondary lymphoid organs
lymphoid organs and T cell development
Thymus – t cells develop, released if don’t recognize self and become cytokines and cytotoxins
lymphoid organs and B cell development
Bone marrow – b cells develop, released if don’t recognize self and become antibodies (different classes)
B cell development in bone marrow
- Precursors in bone marrow
- Self-tolerance in immature B cells
- Mature naïve B cells enter circulation and peripheral lymphoid tissues
- Naïve B cells are short-lived – 50 million per day are made in a mouse
- Stimulated B cells (memory cells) are long lived
B cells and antigens
B cells recognise antigens in their native form – can bind directly to the pathogen/antigen on pathogen surface
T cells and antigens
need to have information about that pathogen processed and presented to them – does this through presentation through major histocompatibility complex class 1 or MHC class 2 (in humans call is human leukocyte antigen class 1 or HLA class 2 Depending if it is presented by MHC/HLA 1 or 2 depends what T cell becomes activated
T cell development in thymus
If T cell recognizes in a strong fashion (strong binding) what is being presented to it, will die - autoimmunity
If no interaction probably means has no recognition of the MHC/HLA on surface – deleted
Low interaction with MHC/HLA these cells are enabled to go out into circulation, these can then mature
what do T cells develop into
Depending what it interacts with will depend whether it becomes a helper or cytotoxic cell
- recognizes peptides in low affinity form on MHC 2 = CD4 helper T cell (only this bind to HLA 2 to allow it to become activated)
- recognizes peptides on HLA 1 = CD8 cytotoxic T cell
secondary lymphoid organs
e.g. lymph nodes, spleen, gut-associated lymphoid tissues
Adaptive immune system
B and T cells kept here so pathogen can be brought here and right ones activated
Secondary lymphoid organs – lymph node
Lymphocytes blood enter
So right and t and b cell can be activated
T and b cells proliferate the germinal centers expand
Afferent lymphatic vessel bring info about pathogen in – afferent comes into the lymph node
In lymph node they activate T cells (provide help to activate B cells)
lymph nodes - phagocytosis
Fragments of bacterium also get taken to the lymph node when broken from phagocytosis – fragments recognised by B cells
Efferent lymphatic – take info elsewhere
Cells of immune system come in blood circulation
Blood cells can meet tissue pathogens find right t and b cells
T cell rich area – inner cortex
B cell rich – germinal center
Secondary lymphoid organs – spleen
Spleen filters the blood as circulates around the body
Not in tissue so can’t go to lymph nodes e.g. if mossy bite the spleen filters the blood to activate the adaptive immune system
Traps blood borne pathogens
Similar structure to lymph node but doesn’t have lymphatic system in and out – has blood circulation through it
Secondary lymphoid organs – GALT/MALT
Mucosal surfaces - pathogen entry
Eat something – need lymphoid organ if comes via mucosal surface
M cell delivers info about pathogen to the GALT
T cell and b cell rich areas
T cells activate the B cells to produce appropriate immune response
no afferent but is an efferent lymphatic -cells can leave GALT and get back into circulation, if pathogen gets into tissues elsewhere in body can effectively clear it
Lymphocyte recirculation
blood circulation, cells coming in as a pool and circulating around the body -cells leave blood circulation to go to lymph nodes via high endothelial venule (HEV) which expresses receptors on its surface that enable the un-activated naïve cells to leave blood circulation and enter lymph node
Spleen constantly filtering pathogens in the blood and getting cells from the blood
