7. Acquired immunity B and T cell development and Ag recognition Flashcards
common precursor of lymphocytes
- multipotential haemopoetic stem cell (haemocytoblast)
- common lymphoid progenitor
- small lymphocyte
- B cell and T cell
- plasma cell from B cell
what stimulates the differentiation of the haemocytoblast into the common lymphoid progenitor?
IL- 7
what stimulates the differentiation of common lymphoid progenitor into small lymphocyte?
IL-7
what stimulates small lymphocyte into B cell?
IL-4
what stimulates small lymphocyte into T cell?
IL-7 and IL-2
what occurs in SCID?
T/B cells cannot be produced - immunodeficiency
what mutation causes SCID?
Mutations in IL-7
where does the development of lymphocytes occur?
bone marrow
Describe B cell receptor
antibody embedded in cell membrane
Ig alpha and Ig beta - has ITAM tail
Describe T cell receptor
Membrane bound alpha and beta
CD3
ITAM tails
what does a T cell receptor recognise
Ag presented by MHC
How do B cells recognise Ag?
on microbe themselves
how do Th cells recognise Ag?
Ag presented by APC
how do Th cells recognise Ag?
Infected cells presenting Ag
general effector functions of B cell - 3
complement, inflammation, phagocytosis
general effecter functions of Th cels
releases cytokines - activate macrophage, inflammation and activation of T/b cells
which 2 cells have the general effector function of killing cells?
Tc cell and NK cell
effector function of Regulatory T cell
suppression of immune system
where do B cells mature?
Bone marrow
where do T cells mature?
Thymus
describe maturation process of T cells
- bone marrow
- migrate to thymus
- enter thymus cortex as thymocytes
- travel down into medulla thymus
- recieve maturation signals by macrophages, dendritic and epithelial cells
B cell 2nd LT
spleen, mucosal tissues
T cell 2nd LT
spleen, mucosal tissues, lymph nodes
how to B/T cells enter/leave lymph nodes
enter - afferent vessels
leave - efferent vessels
difference between antigen dependent and independent phases of development?
independent - primary LT
circulating lymphocytes to detect Ag
Dependent - Secondary LT
after Ag stimulation - produces effector and memory cells
which types of Ag do B cells recognise?
intracelullar - bacteria, fungi, protozoa etc
what is an epitope?
region of antigen specifically recognised by an Ab binding site (paratope)
what is a linear epitope?
AA sequence
what is a 3D epitope?
AA chain wrapped around itself - only exposed AA are recognised
what is a hapten?
small organic molecule which is too small to be recognised by the immune system
when are haptens dangerous?
when they bind to our cells - cause autoimmune response
which secondary LT do Ag in tissue travel to?
Local lymph nodes
which secondary LT do Ag in blood travel to?
spleen
which secondary LT do Ag in gut travel to?
Peyer’s patches
what cells transport Ag to secondary LT?
dendritic
3 types of APC
B cell, dendritic , macrophage
which ag does each APC recognise?
B cell = microbial toxin
dendritic = viral
Macrophage = bacterial
which APC is present in thymus cortex?
dendritic
Which MHC complex does Tc cells recognise?
MHC I
Which MHC complex does Th cells recognise?
MHC II
what causes swollen lymph nodes?
increased migration of lymphocytes to secondary LT as a result of infection
2 types of effector T cells
Th and Tc
cells which express CD4+
Th
cells which express CD8+
Tc
function of Th (4)
- release cytokines
- activate phagocytosis
- activate tc
- promote Ab production
function of Tc
directly kill cells harbouring microbes
specific name of cytokines which Th release
Interleukin’s
where does the activation of Th occur?
peripheral LT
describe the 3 interactions between the Th cell and the dendritic cell
- CD4+ and MHC II
- CD28 and B7
- Cytokines; IL-12
what occurs after the Th cell is activated?
- migrates to site of infection
- released IFN-gamma
- attracts and attaches to macrophage
- IFN-y attaches to IFN receptor
- CD40 ligand attaches to CD40
2 ways a Tc kills cells?
- perforin
2. fas ligand
what 2 cells circulate in the circulating T cell pool
- Thymus-derived naive T cells
2. memory cells
describe composition of circulating T cell pool in babies
more naive cells than memory cells as not been exposed to many memory cells
describe composition of circulating T cell pool in adults
more memory cells than naive cell - less effective at responding to new pathogens
2 types of self tolerence
central and peripheral
where does central tolerance occur
thymus
where does peripheral tolerance occur
secondary LT
describe process of central tolerance
- naive cells enter thymus
- cells exposed to self-Ag
- if cells respond - clonal deletion - apoptosis
describe process of peripheral tolerance
- regulatory T cell recognise cells which attack self-Ag
2. RTC send out cytokines to attract Tc cells to action against them
