T CELL lymphocyte , its function, production and types pptx

T CELLS
Dr SHEMEERA SAIDALAVI VP
PG RESIDENT

CONTENTS
◦INTRODUCTION
◦DEVELOPMENT AND MATURATION
◦T CELL DIFFERENTIATION/ DIFFERENT TYPES
OF T CELLS
a)CD4+T HELPER CELLS
b)REGULATORY T CELLS
c)CD8+ CYTOTOXIC CELLS
d)MEMORY T CELLS
◦PHASES OF T CELL ACTIVATION

INTRODUCTION
 T cells : Type of blood cell
 Belong to a group of white blood cells (WBCs) called lymphocytes.
WBCs protect the body from infection  T-cells is to fight infection.
Along with other WBCs, they play a major role in the immune system,
which guards the body against infection.

T cells are
formed
in BM
migrate to
the cortex of
the thymus
maturation
in an
antigen-free
environment
2–4% of the T
cells succeed
96–98% of T cells
die
by APOPTOSIS
and
are phagocytosed
by macrophages
in the thymus
Lymphopoiesis for T cells

96–98% of T
cells die
by
APOPTOSIS
Intensive screening
to make sure each
thymocyte has the
ability to
recognise self
peptide: self MHC
complex

1
• THYMUS
2
• PERIPHERAL BLOOD
3
• SECONDARY LYMPHOID
ORGANS(paracortex of LN & PALS in spleen)

CONTENTS
◦INTRODUCTION
◦T CELL DIFFERENTIATION/ DIFFERENT TYPES OF T
CELLS
d)MEMORY T CELLS

T CELL - THYMUS
◦ Immature lymphocytes leave the bone marrow  thymus where they
are “educated” to become mature T-lymphocytes.
SCHOOL FOR
TRAINING
NURSE CELLS

LET’S DISCUSS :3 WEEKS TRAINING

WHY VDJ rearrangement?
T CELLS NEED
DIVERSITY

◦ TCR genes undergo rearrangement 
results in diversity of TCR genes to
interact with different peptides
◦ First beta chain of TCR gene is
rearranged  eventually and
sequentially alpha chain also ( not at the
same time)
Mature TCR-αβ are formed

DP cells  recognize the
MHC bound peptides ( first
degree of training &
screening)
MHC class I/ MHC class II
2 DISTINCT SELECTION PROCEDURE
CORTEX

◦ POSITIVE SELECTION: thymic epithelial cells ensure that the DP cells
learned how to recognise the MHC molecules  ENSURE MHC
RESTRICTION
◦ NEGATIVE SELECTION : Those high affinity interactions are
removed Ensures SELF TOLERANCE is maintained and there is no
autoreactive T cells are generated
Negative selection failed in many
autoimmune diseases

◦ In the first selection round  just learn to recognise or gets familiarize
with the MHC bound peptides  these peptides are self peptides
produced by thymic epithelial cells
90% die

◦ Now cortical part of maturation is over migrate to medulla  interact with
medullary epithelial cells  start recognizing class I &class II MHC molecules

Thymic maturation almost over
Descent further down to medulla reaches HEV
Migrate all through the body and they posted to
peripheral lymphoid organs(LN,spleen)field of
action  further T cell differentiation and
maturation

LYMPH NODE
◦ After thymic selection T cells become  naïve T cells
Class II
MHC
Class I
MHC

CD4+T HELPER CELLS
◦ Develop in BM THYMUS (training )
 naïve T helper cells move to LN
 activated by APC
◦ After activation T cell interact with
other cell types / differentiate into
different subtypes

◦ APC (Dendritic cells, macrophage )  along with pathogen  go to LN  interact
with naïve T helper cells
◦ Depending on the polarizing cytokines they released  naïve T helper cells
differentiate into several subtypes

Depending on type of cytokine + the
type of master regulatory gene gets
expressed + type of infection
All 3 determine
how a T cell further
categorize into
different subtypes

◦ If T reg cells are absent  balance
move more towards the
inflammatory responses
increases chance of severe
inflammation + autoimmune
disorders  DANGEROUS

CD4+ T helper cells
Some of CD4+ T helper
cells become T reg
cells

How it
different from
CD4+T helper
cells
CD25

◦ Once CD4+T helper cells  switch
into T reg cells they maintain the
level of Fox p3 throughout their life

◦ Maintenance of Treg
identity depends on signals
from IL2R α, TCR, TGF β
Increases Fox P3

T-reg cells has anti inflammatory function
◦ T reg interact with macrophage  prevent it
from interaction with other CD4+ T helper
cell
◦ T reg directly compete with CD4+ T helper
cell for IL-2 (IL- 2 is necessary for the devp.
of both cells)
If IL-2 is low CD4+
T cell do not develop
that much
Macrophage  secrete proinflammatory cytokines like IL1
& IL6  regulate and activate CD4+ T helper cells 
thereby activate other immune complex

Perforin granzyme
pathway
Compete for IL-2
Directly inhibit
macrophage
Immunosuppressing
agents

T reg cell suppress function of APC

T reg : prevent early onset of
autoimmune disorders by
providing its anti inflammatory
resposes

CYTOTOXIC T CELLS
◦ Cytotoxic T cell has CD8 co-receptor

◦ Perforin creates pores Thereby
granzymes enter the cell
◦ Interaction b/w cytotoxic T cell & target
cell
1. FAS-FASL mediated interaction
2. Perforin – granzyme mediated
interaction

◦ DEATH of virus infected cells
 eliminate the virus

◦ Memory T cells  less stringent
reactivation criteria ie, they gets back
to the cell cycle and proliferate rapidly
◦ Naïve T cells cant proliferate rapidly
until it is activated by APC
◦ Memory T cells quickly gets activated
by APC

CD8 + cells that are
very tired

◦INTRODUCTION
◦T CELL DIFFERENTIATION/ DIFFERENT TYPES OF T
CELLS
d)MEMORY T CELLS

PHASES OF T CELL ACTIVATION
1.Activation phase
2.Clonal expansion
3.Effector phase
4.Declining phase
5.Memory phase

Few cells remain
will become the
memory T cells
Following second attack  these memory cells can
easily identify attacking pathogen and become
secondary effective T cells easily kill them

T CELL lymphocyte , its function, production and types pptx

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Editor's Notes