B cell & T cell development

Y.Guilloux

what is the primary lymphoid organ (LO) of B and T lymphocytes

Bone marrow : pluripotent hematopoietic stem cells →

• B lymphocytes : bone marrow ( I lymphoid organe)

• T lymphocytes : Thymus ( ILO )

what type of selection occurs in the bone marrow (ILO) for B lymphocytes

negative selection

what type of selection occurs in the thymus (ILO) for T lymphocytes

negative and positive selection

what are the 2 types of T cells

1. αβ : TCR chain are made up of α and β chains

2. γδ : TCR chain are made up of γ and δ chains

what is the order of V(D)J rearrangement for T lymphocytes

1. VDJ rearrangement of the DNA of the β and δ chains

2. VJ rearrangement of the DNA of the α and γ chains

when does the surrogate light chain intervene in the B cell development

during the large pre B cell stage

when does negative selection/clonal deletion occur in B lymphocytes

when a B cell recognises a self antigen

what is the name of MHC (major histocompatibility complex) molecules in humans and mice

HLA = MHC molecule in humans

H2 = MHC molecule in mice

what are the 3 classes of MHC class I molecules in humans

HLA A/B/C

what are the 3 classes of MHC class I molecules in mice

H2 K/L/D

what are the 3 classes of MHC class II molecules in humans

HLA DP/DQ/DR

what are the 2 classes of MHC class II molecules in mice

H2 IA/IE

what does it mean if the nomenclature/haplotype of the MHC is H2b

it means that all the MHC molecules have the allelic form of b (homozygote), so :

• H2 Kb/Lb/Db (MHC I)

• H2 IAb/IEb (MHC II)

what does it mean if the nomenclature of the MHC is H2b/d

it means that all the MHC molecules have the allelic form of b/d (heterozygote), so :

• H2 Kb/Lb/Db and Kd/Ld/Dd (MHC I)

• H2 IAb/IEb and IAd/IEd (MHC II)

what experiment shows that self tolerance of MHC

Spleen cells are isolated of Mouse with haplotype H-2ᵏ

mouse w/ same haplotype is injected with spleen cells H-2ᵏ from previous mice

→ No immunisation as H-2ᵏ is self MHC so

• B and T cells specific for H-2ᵏ were deleted or inactivated during development

next ,

Spleen cells are isolated of Mouse with haplotype H-2ᵏ

mouse w/ H2^d haplotype injected w/ spleen cells H-2ᵏ from previous mice

→ immunisation and Serum contains anti–H-2Kᵏ antibodies as H-2ᵏ is foreign (allogeneic) to an H-2ᵈ mouse

• T-cell help is available → B cells are activated

how is a transgenic mouse that recognises self Ag produced in the lab

mouse w/ H2k haplotype crossed w/ H₂^d Tg Ig anti H₂-K^k Ab mouse that has BCR that recognises self Ag not expressed in the mouse → H2^d/k Tg anti H₂-K^k Ab ( transgenic mice that recognises self Ag)

so in the H2^d/k Tg anti H₂-K^k Ab mouse (B cella against self Ag)

n mature B cells express anti K^k (self Ag) ans the BCR that recognises self Ag are deleted in the bone marrow due to negative selection

if self Ag recognised by B cell how does receptor editing allow the negative selection of B cells

after detection of autoreactive B cell → light chain rearangement unit productive rearrangement occurs → B cell can now leave bone marrow to II LO

what is an anergic state of a B cell

self reactive B cell remains alive but unable to be activated

to prove clonal anergy in mature B cells a HEL mouse (chicken egg white lysozyme) crossed w/ anti-HEL showed what results

this crossbreeding → double transgenic Tg carrying both HEL and anri-HEL transgenes and what is observed :

• theres still the presence of HEL binding B cells but little to no IgM expression → anergic B cell

so what are the 3 main mechanisms if autoreactive B cell is detected

1. apoptosis

2. Anergic B cell

3. Mature B cell clonally ignorant

On BCR and TCRs there are structures associated to them that contain an ITAM domain, what do they allow

receive phosphorylation = phosphorylation domains

• allows signal transduction

• can bind w/ protein w/ 2 SH2 domains

what structures are ITAM found in B and T cells

CD79α and β : B cells

CD3 : T cells

how does the Fab fragments of Ab binding to BCR alter the signal in B cells

• Fab fragment of Ab bids to BCR but no crosslinking of BCR → no signal

• Fab fragments crosslink BCR [F(ab)2] → weak signal

• anti-F(ab)2 Ab cause extensive cross-linking → strong signal

what does a cytoxicity assay mesure

quantifies target cell death caused by cytotoxic immune mechanisms, most commonly by CD8⁺ cytotoxic T lymphocytes (CTLs) or NK cells

if a H₂^b mouse is immunised by a virus and the T cells are isolated from spleen, what would the cytoxicity assay show compared to an uninfected mouse

infected mouse : high percentage of lysis for only MHC of the haplotype H₂^b will recognise and kill the virus

infected : no lysis as theres been no infection

the 3 CDRs recognises specific structures (MHC, peptide), which CDR recognises what ?

CDR1 : recognises MHC-peptide

CDR2 : recognises the MHC only

CDR3 : recognises peptide only

what is the positive selection of T cells

in the thymus : the survival of T cells that recognise self MHC molecules

what cytotoxicty assay is observed if a heterozygote mouse H2^a/b is infected w/ a virus

T cells kill infected target cells presenting antigen on:

• H-2ᵃ

• H-2ᵇ

what cytotoxicty assay is observed if a heterozygote mouse H2^a/b that is irradiated and grafted w/ a thymus from H2^a mouse which is infected w/ a virus

• irradiation of the mouse is to remove all hematopoietic cells (HSCs)

• Graft a thymus from an H-2ᵃ mouse : Thymic epithelial cells express only H-2ᵃ

• HSCs from H2^a/b are injected in the mouse

→ T cells kill infected target cells presenting an Ag on H2^a

Only T cells whose TCRs can bind H-2ᵃ survive = positive selection (T cells capable of recognising H-2ᵇ die by neglect)

Spleen cells from an H-2ᵏ mouse are isolated and transferred into two recipient mice, one H-2ᵏ and one H-2ᵈ. In which recipient will the transferred T cells function, and why?

The transferred T cells will function only in the H-2ᵏ recipient, because they are MHC-restricted to H-2ᵏ and can recognise antigen presented on H-2ᵏ MHC molecules. In the H-2ᵈ recipient, the T cells will not respond because they cannot recognise antigen presented on H-2ᵈ MHC.

what MHC class does CD8+ T cells recognise

MCH I

what MHC class does CD4+ T cells recognise

MHC II

what type of cells present MHC I and II

MHC I : all nucleated cells

MHC II : professional APCs s B cells, macrophages and dendritic cells

what is negative selection

the deletion of developing T cells w/ TCRs that recognise self peptide-MHC complexes w/ high affinity