how does blood enter the lymphatic system
1) it must leave the blood vessels, leave the endothelial wall and move into the tissue to become interstitial fluid
2) this is how we see swelling during injury
3) eventually it is pushed from the tissue into lymphatic vessels where it becomes lymph
4) the thoracic duct then returns the lymph to the cardiovascular system
what are the antigens delivered to the lymph nodes
non-self (from infection) and self (your own cell debris)
can our lymph nodes be infected
yes - in a bad infection, living pathogens can enter the lymphatic system and infect
describe what happens with lymphatic vessels as infection gets worse and worse
1) as infection spreads through layers of tissue, it reaches blood vessels
2) this triggers local activation of the blood vessels
3) increased vascular permeability allows plasma to leak out into the tissue, raising interstitial fluid volume
4) also enables the recruitment of blood-borne neutrophils and monocytes/macrophages
5) resulting swelling pushes material from the tissue into the lymphatic vessels
what happens to your lymph node during an infection
they grow in size and can become painful
how does swelling during infection help
pushes antigens, cellular debris, immune cells and plasma into the draining lymphatic vessels
describe how lymph enters a lymph node
1) swelling pushes material from the tissue into the lymphatic vessels
2) these lead directly to lymph nodes
3) lymph nodes have afferent (enter) and efferent (exit) tubes going into them
are t-cells specific
yes: each t-cell has a unique t-cell receptor, so a single t-cell can only recognise one antigen
what are t-cells activated by
only antigen presenting cells
how are b-cells activated
they can recognise antigens as free proteins
where are b-cells and t-cells found
lymph nodes:
- b-cells: outer areas of lymph nodes
- t-cells: inner areas of lymph nodes
are t-cells and b-cells together or separated
separated, but at some point they must come together
what are b-cell antigens usually
full length proteins that fit into its receptor
describe the process of lymph flow through a lymph node with regards to b-cell activation
1) lymph moves through the sinus region of the lymph node
2) the lymph goes through smaller and smaller conduits (vessels)
3) some of the lymph percolates through the b-cell zone
4) when the correct antigen arrives, the corresponding b-cell is activated
describe how a b-cell is activated through an antigen
1) the b-cell “grabs onto” its antigen with its receptor, which activates a signal transduction through the receptor
2) then, the BCR is endocytosed
3) the antigen that was a full-length protein is cleaved into small fragments and packaged into vesicles inside the cell
5) the b-cell presents the small fragments on its surface via MHC class II molecules
6) the b-cell moves towards in the inner areas of the lymph node so it can reach a t-cell to present the antigen to
7) the t-cell receptor, too, is specific to the antigen fragment and recognises the peptide-MHC II complex
8) once the t-cell recognises the fragment, it produces cytokines that trigger the proliferation of that b-cell
how do b-cells and t-cells know where to go/find each other
signals by chemokines in the lymph node, laid out by other cells
what do CD40 receptors do
- on the activated helper t-cell binds CD40 on the b-cell
- this is the critical co-stimulatory signal necessary for b-cell activation
what do cytokine receptors do
- t-cell secretes cytokines which bind cytokine receptors on the b-cell
- these drive proliferation and influence what antibody class the b-cell will eventually produce
what are the types of t-cells
- CD4: Tfh cells aka helper cells that coordinate the immune response by activating other cells
- CD8: cytotoxic t-cells that directly destroy infected cells
what is linked recognition
process where b-cells and T-helper cells recognize different parts of the same antigen to activate a high-affinity antibody response
what does linked recognition occur for
thymus-dependent antigens: antigens that are typically soluble proteins and require cooperation between b-cells and t-helper cells
what happens after the t-cell and b-cell have interacted
the b-cell is “told” it needs to migrate back to the follicular (outer) area of the lymph node, where it becomes a germinal centre
what happens at the germinal centre
the b-cell, after interacting with the t-cell, undergoes proliferation to finally produce antibodies specific to the antigen
what happen without linked recogntion
- not enough b-cell proliferation
- no long-term memory populations of b-cells
- small amount of antibodies produced
