Development of b and t cells

• each lymphocate carries an AG receptor with a unique specificity

• AG recognition by a specific lymphocyte triggers its activation and proliferation

• daughter cells carry identical AG receptor to the parental cell (=clone)

• one specific lymphocytoe trapped/slected - gets active an proliferates (1/1000000) all the daughter cells who arise arry aG receptor of parental cell.

• Clonal selection - selection of one cell

• clonal proliferation - proliferation leads to gen. identical clone of daughter cells

• One t-cell can be specific for peptides for different pathogens

• how fast is the reproductive rate of T cells - not clear (4-7d)

• per cell division -> few hours

• leads to elimination of infection

• exponential increase after threshold for protection is reached

double pos - have CD4 and CD8 -> bc important for TCR signal, must interact with MHC/self peptides

ensures posibility of positive selection.

single pos - either CD4/CD8

single neg - no CD5 or CD8

negative selection latest (small resting single-pos. thymocytes)

somatic cells of the body - when does recombination takes place - 1. crossing over = increasing diversity -> germ line; 2. cnacer cells -> somatic line! just wants to differentiate and proliferate

Problem: how could you combine the sections ? later on mRNA lever -> but still large genome => recombination in genome -> somatic recombination on DNA level

high number of V/J segemnts - high variety of AGs. -> LC - only 1 recombination event here - one J with one V

3 kind of gene segemnts for HC -> 2 recombination events here - 1 D with 1 J - 1 V with 1 DJ.

sequencial process - does not take place on the same time.

afterwars transcritoption, splicing, translation and protein synthesis - normal

ß comparable to VDJ

a comparable to VJ

Process always in beginning: Germline gene configuration in maturing CD4-8- thymocyte ->Dß-Jß rearrangement (y and sigma chain rearrangement may also occur) in CD25+ CD44^lowthymocyte rearranging ß-chain genes -> Vß -DJß rearrangement in frame. ß chain protein produced - in CD25+ CD44^low thymocyte cytoplasmic ß+ ->surface expression of ß chain with durrogate a chain. ß rearrangement stopf cell proliferates CD4/CD8 induction a transcription starts - in CD4- 8- ->CD4+8+ -> Va-Ja rearrangement - surface expression of a:ß:CD3, selective events begin -> in CD4+8+

positive selection does take place in double neg. stage - immediated by taq.

how do we get to the signel positive stage? positive selction can develope in CD4 or CD8. the other one will be downregulated

normal MHC 2 expression -> both CD8 and CD4 T cells mature (by epithelia cells)

MHC2 negative mutatnt (knock out of MHC2 processing -> only CD8 Tcells mature

mutant with MHC 2 transgene expressed in thymic epithelium -> both CD8 and CD4 T cells mature (rescue mutant)

Mutant with MHC2 transgene expressed that cant interact with CD4 -> only CD8 T cells mature

MHC2 = B cells, macrophages, DCs and epithelia cells -> absolutley needed for CD4 development

first always heamapoetic stem cells -> pluripotent.

B cell precursor rearranges its immunoglobulin genes -> generation of B-cell receptors in the bone marrow

immature B-cell bound to self cell-surface AG is removed from the repertoire -> negative selection in the bone marrow -> autoreactive B cells recognize

matture B cell bound to foreign AG is activated -> B cells migrate to the peripheral lymphoid organs

Activated B-cells give rise to plasma cells and memory cells -> AB secretion in bone marrow and lymphoid tissue and memory cells in lymphoid tissue

=> B cells need to be negative selected.

somatic cells of the body.

when do recombination takes place?

• crossing over = increased diversity -> germ line!

• cancer cells -> somatic line -> just wants to differentiate /proliferate

• problem: How could you combine the sections? -> later on mRNA level -> but still large genome

• => recombination in genome

• somatic recombination on DNA level!

Germline DNA—somatic recomb. -> D-J joined rearranged DNA—>V-J or V-DJ joined rearranged DNA—> Primary transcript RNA—Splicing—>mRNA—Translation—> polypeptide chain

what is somatic recombination? (Exam) -> DNA recombination in lymphocytes -> even on genome level in somatic cells, not restricted to germ cells

gene setments are encoding in human genome.

uncommon - bc recombination event = something unexpected happens

explainatory slide

does this rearangement take place on both chromosomes ? first rearrangement - yes, on both

how often is the cutting of DNA successful ? -> endonucleases (restrictions enzymes) cut and generate blund ends - problem -> V needs to find D segement; changing of gen. code - funcitonal protein ?

1/3 is working - 3 bp encode a AS - cant derive

2/3 unproductive rearrangement & no AB production

first HC in parallel for both chromosomes

allelic exclusion - means of molecular biology - rearrangement only on 1 chromosome at a time

B cell maturation -> ATP dependend

to prevent cell-loss!

only for LC gene-segments.

increases numbers of probability for sucessfull recombination but only on LC

opportunities to prevent loss of Bcell = increase number of recombination event on one chromosome -> frame shift would be unproductive.

icrease probability of successful recombination event

immature B cell (bone marrow) - shoud be selfactive

1. multivalent self molecule - crosslinking with AB (igM)-> clonal deletion or receptor bindng -> apoptosis (normally) or receprot additing (rescue) -> normally or receptor additing (rescure)

2. Soluble slef molecule ( b cell does recognize molecule, but without crosslinking -> survive but anergic => cant be activated again!) —migrates to periphery -> Anergenic B cell

3. Low affinity noncross-linking self molecule (most complex -> maybe a bit of recognition, very weak binding, less as when the cell gets anergic) -> migrates to periphery -> mature/ naive B cell (very clonally ignorant) => mainly potential autoreactive = could cause autoimmunereaction! =>crossreactivity

4. No self reaction (doesnt recognize) -> migrates to periphery ->Mature/naive B cell -> mainly potentiall autoreactive = could cause autoimmune reaction -> cross reactivity - prinicpal the same as ‘3’ -

not yet been stimulated

hasnt seen the AG yet

same as ‘mature’ but he doesnt like that term

activated by self recognition

still alive but not able to do anything

hard to activate

process of aging, similar to anergy

(only for LC) -> strong ligation of IgM by self AG -> Arrest of B-cell development and continued light chain rearrengement: low cell-surface IgM (still active) -> a new receptor specifity is now expressed —2 ways—> 1. if the new receptor is still self-reactive, the B cell undergoes apoptosis. 2. if the new receptor is no longer self-reactive, the immature B cell migrates to the periphery and matures

only one time possible still during selection process

a way to safe resourcess -> could go into apoptosis

another LC recombination

thymus= branch between lungs

basically the same progress

• starts in the Thymus: T cell precursor rearranges its T-cell receptor genes in the Thymus -> T-cell progenitors develop in the bone marrow and migrate to the thymus.

• Immature T-cells that recognize self peptides MHC molecues receive signals for survival. those that interact strongly with self AG are removed from the repertoire. -> positive (first )and negative (second) selection in the thymus

• mature T cells encounter foreign AGs in the peripheral lymphoid organs and are activated -> mature T cells migrate to the peripheral lymphoid organs -> AG presentation

• activated T cells proliferate and migrate into peripheral sites to eliminate infection -> activated T cells migrate to sites of inflammation -> T cell differntiation

the ones self recognizing killed

second

with loaded

=> apoptosis

in the inner part of the medulla/thymus

recognize MHC molecules - T cell only continues development if it interacts with MHC molecules! also with loaded self peptide molecules

but must not interact with MHC PEPTIDE/Self peptide

first

takes place in the outer part of the medulla

• Located above the heart

• cortex (=outer area) contains cortical epithelia cells, immature thymocytes (developing B cells), and macrophages

• medulla (=central area) contains medullary epithelia cells, mature thymocytes, and DCs

• fully developed in cortex.

• negative selection mainly presented by DCs

• cortex outer part of thymus, medulla inner part of thymus -> only here negative selection