T-cell development and differentiation

T-cell diversity is generated in the thymus The TCR is a recognition unit that looks like an arm of the BCR In which the μ and β chains, and the light chains and the α-chains are homologuos The main mechanisms of gene rearrangements are similar for the TCR and BCR CDR1,2, 3, loops in theTCRα and TCRβ chains

A T-cell precursors migrate from the bone marrow to thymus

T-cell markers are induced after thymocytes interact with the thymic epithelial cells

A Notch-1receptor and its cytoplasmic region, acting as a transcription factor is required for the development of the T-cell lineage

Less V-segments, but the Delta-chain has large junctional diversity Vg9Vd2 T cells can recognize PAgs (such as isopentenyl pyrophosphate, IPP) that are accumulated in tumour cells Pags: natural phospho-antigens Az αβ and γδ T-cells recognize different antigens 1-5 % of T-cells in the blood But γδ T-cells are the dominant type in epithelia Unlike αβ T-cells recognition of antigens by γδ T-cells is independent of MHC. They recognize phosphorylated metabolites produced by many microbes. Tumor-specific immune response

Multiple functions of gamma-delta T cells. NK funkciók Stressz-related proteinek felismerése British Journal of Haematology, 2013, 160, 123–132 doi:

Generation of T-cell receptor diversity mehanizmusa (occurs in the thymus) Si milar to that of B cells’… BUT!! 1.No diversification after activation 2. No secreted form

Diversity of the BCR and the TCR

The αβ and γδ T-cell lineages develop from a common precursor

A β-chain rearrangement (like Ig heavy chain) A TCR-rearrangement—similar to BCR Efficiency of beta chain rearrangement is about 80% RAG-1 RAG-2 genes become are inactivated Timocyte proliferation CD4, CD8 expressionó

The α-Chain rearrangement (Ig light chain) TCR-rearrangement is similar to that of the BCR

C mIg H mIg L TCR  TCR  T-CELL  C V T cell receptor TCR B- AND T-CELL RECEPTORS SHARE BASIC STRUCTURE TCR =  +  The variable region of the  -chain is generated by gene rearrangements of the V – D – J gene segments analogous to the generation of IgH diversity The variable region of the  -chain is generated by the recombination of V and J analogous to IgL Single binding site No somatic mutation

Main steps of T-cell development, gene rearrangemnts, changes in gene expression

Shaping the T-cell repertoire. Positive and negative selection Thymus

Few TCR reacts with the MHC (about 2%) most T-cells die of neglect. ( no survival signals) α-chain rearrangement can continue until the assembly of a functional αβ receptor has been assembled.

Selection of developing T-cells in the thymus Bare lymphocyte syndrome MHCI vagy MHCII deficiency Lack of CD8+ or CD4+ cells Role of co-receptors in the development of single + T-cells

DC Macrophage in medulla of Thymus. Special transcription factor expressed… AIRE. Tissue spec. Antigens expressed AIRE mutaton: Autoimmune polyendocrinopathy -candidiasis-ectodermal dystrophy

Multiple stages of T-cell development in the thymus

CD25+ FoxP3+ cells FoxP3-deficiency: autoimmune disease IPEX: immune dysregulation polyendocrinopathy, enteropathy, X-linked syndrome

T-cell activation

ANTIGEN BINDING NO INTERACTION APC T CELL AKTIVATION Antigén receptor T-CELL B-CELL Characteristics of antigen recognition by T-cells (TCR) 1.T-cells need antigen processing by APCs 2.T-cells recognize virus-infected cells

Phases of T cell response (review)

α βα β ε δ ε γ ζ ζζ ζ ITAM Immunoreceptor Tyrosine-based Activation Motif ACTIVATION A T-CELL SIGNALING IS INITIATED BY PHOSPHORYLATION OF ITAMs

Clustering of the T-cell receptor and a co-receptor initiates signaling within the T cell.

TCR signaling (review)

THE IMMUNOLOGICAL SYNAPSE

T SEJT APC

interactionRecognition/activation stabilization detachment Negulescu P.A. et. al. Immunity 4: , 1996 T SEJT – ANTIGÉN PREZENTÁLÓ SEJT KÖLCSÖNHATÁS Ca-influx detectable in minutes by the changing colour of a Ca-sensitive dye

AZ IMMUNOLOGICAL SYNAPSEÓGIAI SZINAPSZIS T SCELL ANTIGEN PRESENTING CELL CD48 CD2 ICAM-1 LFA-1 B7 CD28 CD4 SIGNALING COMPLEX adaptor ACTIVATED T CELL

T cell APC THE IMMUNOLOGICAL SYNAPSE

CELL ADHESION AND SIGNALING IS FACILITATED BY MANY RECEPTOR- LIGAND INTERACTIONS * * * * * * APC T CELL MHCI – CD8 MHCII – CD4 CD40 – CD40L B7 – CD28

T-cell activation requires two signals APC Th Signal 1 antigén & antigén receptor Signal 2 B7 FAMILY (CD80 & CD86)CD28 AKTIVÁCIÓ The professional APCs (dendritic cells, macrophages, B-cells) express or upregulate co-receptors that deliver the 2nd signals. Regular tissue-derived cells fail to express co-receptors

Second signals triggered by co-receptors are required for T-cell activation CD40 CD40L B7 CD28 ACTIVATION