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T-cells require activation to carry out their function effectively.
e.g. activation of naive CD4+ T cell by antigen presenting cell

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TC kills infected cells (or tumour cells) through secretion of perforin and granzymes or activation of death receptor. Requires participation of TH and cytokines to generate large pool of memory TC

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T cells are activated when presented with MHC class molecules. Once T cells are activated they release cytokines

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T cell is activated depends on:
Class I MHC (bound by TCR on CD8+)
Class II MHC (bound by TCR on CD4+ T cells)

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2 different types of naive T cells
--> CD4+ and CD8+
each of these 2 T cells have different signals for activation

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Two subsets of T cells: CD4+ & CD8+
Two signal required for activation of T cells : TCR and costimulation
Antigen presenting cell(APC) such as dendritic cells, macrophages & B cells present peptide antigen on MHC to naive T cells at lymph nodes

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t cells have t cell receptors on cell membranes, which is used for antigen binding. t cells can be divited to 2 classes, CD4 and CD8

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2 classes of MHC (class I and II)
class I is found in all cell except RBC
class II is found in antigen presenting cells

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Peptide fragments present on the MHC complex of the antigen presenting cell will bind to the T cell receptor of the naive T cell and helper T cell and effector T cell, causing the activation of these T cells.MHC II helps to activate CD8 cells while MHC I helps to activate CD4 cells

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Dendritic cells activate naïve T cells through presenting the pathogen to the lymph nodes. There are two types of T cells, cytotoxic and helper. Each of it has an effector and memory.

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Helper T cells and cytotoxic t-cells.
Co-receptors are
CD-4 for helper
CD-8 for cytotoxic
They are activated by processed antigens presented on Antigen Presenting Cells.

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T cell receptors is used for antigen binding. T cells can be divided into helper T cells (CD4) and cytotoxic T cell (CD8).

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After DCs process the pathogen, they will present the antigen on its MHC, for recognition by T cells.
There are two types of MHC Classes: MHC Class I and MHC Class II
Two main types of T cells:
(Killer) Cytotoxic T cells and Helper T cells

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There are 2 signal process requires for T cell activation. First is the recognition and binding by TCR and CD4. Second is co-stimulation includes cytokines and other co-stimulator. The most important pair are B7 and CD28. The 2 signals activate T cells in which T cells synthesize and secretes cytokines IL-2.

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T cells undergoes activation and differentiation and they are CD4+ and CD8+

The activation of naïve T cells requires 2 signals. The first signal is when the TCR recognizes and binds to the MHC 2 molecule (CD4+) or the MHC 1 molecule (CD8+)
The second signal is co-stimulation, and some common ones are CD28 and CD45

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T-cell activation requires 2 signals.
1st signal: recognition and binding of TCR to the antigen presented
2nd signal: co-stimulation  (B7---- CD28)

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T cells can differentiate into Helper or Killer T cells

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T cell activation is a 2 signal process
1. Recognition and binding by TCR and CD4+ generated the first signal of T cell activation
2. Costimulation which enhances the 1st signal. Without costimulation, T cells which recognised the antigen remain in prolonged state of inactivity
Costimulators include cytokines and pair of plasma membrane molecules. An example is B7(found on APC) and CD28 (found on T cell)

2 types of MHC
- MHC 2 present to CD4
-MHC 1 present to CS8

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1.Antigen-presenting cells goes through Antigen Processing and Presentation to Naive T-Cells to activate them

2. T-Cell receptors and CD4 in a CD4+ T-Cells binds to the presented antigen fragment to start the activation of T-Cells

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2 signals are required to fully activate T cells.

1) TCR recognizes and binds the antigen & CD4+ receptor and binds to MHC II molecule which generates the first signal.

2) T-cell costimulation
- cytokines
- pair of plasma molecules

Without 2nd signal, T cells that previously recognize antigen will remain inactive.

For CD8+, it binds to MHC I molecule.

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glycoproteins
CD4- Th cell ->Th1, Th2, Tfh, Treg, memory Th Cell
CD8- Tc cell-> memory Tc cell, effector Tc cells
(TCR:alpha & beta subunits/ gamma delta subunits)

Co-stimulation
CD28 -APCs to B7-1/B7-2 - resting Tcell

MHC
-CLASS I -(3 alpha and 1 beta) endogenous, ER (all nucleated cell)
-CLASS II - (2 alpha and 2 beta) exogenous, specialised vesicular compartment

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The structure of T cell receptor structure (alpha and Beta chains) : Made up of 2 polypeptide chains that will compose on antigen binding site together.
and it undergoes activation

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1) CD4+ is helper T cell while CD8+ is cytotoxic T cell.
2) Dendritic cells activate Naive T cells

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Activation of T cells involve in TCR present on the T cell surfaces recognizing antigen that is presented on MHC by phagocytes.

2 classes of MHC
MHC class 1 present on other cells
MHC class 2 present on phagocytes