T cells Flashcards
T lymphocyte involved in effector function
cytotoxic T lymphocytes (Tc)
T lymphocyte involved in regulatory immune function
Helper T cells (Th cells)
How T cells react with antigen
T cell Receptor (TcR) - present on T cell membrane surface, derived from bone marrow
CD4+
- expressed by what cell
- interacts with which MHC
- binds with which region of MHC
- coreceptor on Th cells
- MHCII
- beta 2 domain of MHCII
CD3
- expressed by which cells
- important
both Tc and Th cells
important for clonal expansion
How B cells react with antigen
immunoglobulins
TcR look structurally similar to
FAB region on antibody where antigen binds
Two major types of CD4+
Th1, Th2
This specific type of cell modulates phagocytic cell and inflammatory reactions
Th1
This specific type of cell produce factors that help stimulate B cells to differentiate into plasma cells
Th2
TcR recognize what complex
MHCII with a bound processed peptidal antigen on an APC
Rearrangement of T cell receptors occur at this site
Thymus (arise in bone marrow, mature in thymus)
Which step of rearrangement/mode of diversity is NOT present in T cells?
Somatic hypermutation - only in B cells
TcR structure. Which part is equivalent to the heavy chain?
Valpha Vbeta
Calpha Cbeta
beta is like heavy chain
Which part of TcR structure will undergo rearrangement first?
Variable beta chain rearranges first, then produces alpha chain which will undergo VJ rearrangement like light chain
What is the signal that induces Th cell to become a Th1 cell?
IL-12 released from professional APC
Signature cytokine of Th1
interferon gama
After Th cell binds to profession APC, explain in 3 steps how it matures to Th1 cell
professional APC releases IL-12
induces Th to become Th1 cell
Th1 will release interferon gamma
Function of interferon gamma
professional APC (like macrophages) increase production of oxidative species = BETTER KILLER
Important property of interferon gamma
class switch factor. tells B cells to produce IgG for opsonization
When would you develop a Th1?
To produce IgG when macrophage wants to opsonize
Explain in 3 steps how Th2 cell develops
- Macrophage does NOT release IL-12
- Th cell will produce IL-4, feeds back on to itself
- Converts Th cell to Th2
IL-4
Th2
Il-12
Th1
Il-4 is a class switch factor for
IgE
Why would you develop Th2?
To produce IgE, might be more important for parasitic infection, wont ingest it to destroy it
receptor for HIV
CD4+
Marker expressed on Tc cells
CD8+
CD8+
- expressed by what cell
- interacts with which MHC
- binds with which region of MHC
- Tc cel
- MHCI
- alpha 3
A second receptor on T cells encoded from distinct family of genes but with structurally similar polypeptide chains
gamma and delta
When does Tcell activation occur?
When TcR of T cell has engaged processed antigen in context of an MHC on APC
Birthplace of T cells
bone marrow
thymocyte
maturing T cell in thymus
Maturation steps of Thymus
DN>DP>SP>PS>NS
Enters thymus as double negative through which region of thymus?
Cortical region
Double negative
CD4- CD8- TcR- CD3-
T cells undergo beta and alpha chain rearrangement in this region
cortical region (first step)
Transitions from double negative to double positive in this region
From cortical region on way to cortico-medullary junction
This part of TcR undergoes VDJ rearrangement
beta genes
Once beta chain is complete, a small portion migrates to cell membrane via this structure to trigger allelic exclusion
Surrogate alpha chain
This part of TcR undergoes VJ rearrangement
alpha gene
T cells reacts with these to become single positive
MHCI and MHCII
MHC in thymus react with
SELF MADE antigens
Presents peptides from all over by inducing tissue specific genes
Auto immune regulator element (AIRE)
After surviving positive and negative selection, T cells leave through this region of thymus
Medulla
Fate for cells that don’t pass the selection tests in thymus or see antigen
apoptosis
Percentage of T cells that survive the selection test in thymus
5%
These cells exress MHCI and II for purpose of single positive
Thymic epithelial cells
This part of selection ensures Tcell wont engage its own MHC once released
negative selection
process becoming either a CD4+ OR a CD8+ based on interaction with specific MHC
positive selection
This enzyme is not present in T cells so that hypermutation does not occur
AID (activation induced cytodine deaminase)
Occurs by genetic recombination of constant (C) gene segments to synthesize Ig isotypes
Ig class switching
Occurs by genetic recombination of constant (C) gene segments to synthesize Ig isotypes
Ig class switching
