Post on 30-Jul-2015
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1. ComplementSystem
2. Phagocytes (neutrophils, macrophages, mast cells)
INNATE IMMUNE SYSTEM
ADAPTIVE IMMUNE SYSTEM
Lymphocytes: T and B Cells
Lymphocytes are usually defined by where they undergo their “ basic training” ---
Thymus- derived. Bone marrow derived.
T – lymphocytes/ T cells B – lymphocytes/ B cells
Natural killer T/ NKT cells.
Lymphocytes can also be defined by the type of receptor they display on their cell surfaces
TCR BCR / Ig neither- T cells - B cells - Natural
killer cells- NKT cells
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The T cell can be identified by the presence of the CD-3(cluster of differentiation ) molecule which is associated with TCR on the T cell surface.
Two other CD molecules are used to identify CD3+ T cell subsets , CD 4 + and CD 8 +
CD 4 + T CELLS
It accounts for approx. 2/3rd of mature CD3 + cells.
Also known as Helper T ( Th) cells.
CD 4 molecules displayed on the surface of these cells recognize a non peptide binding portion of MHC class II molecules, thus are restricted to the recognition of
p MHC class II complexes.
Subclassification of T helper ( CD 4+ )
T helper 1(TH1)- regulation of cellular immunity.
-Interferon – y, IL- 2.
T helper 2 (TH 2)- helps B cell in isotype switching.
- Production of antibodies. - IL- 4, IL-5,IL-6,IL-10.
Interferon – y inhibits TH 2.IL-4 & IL-10 inhibits TH 1.
CD 8 + T cells
Comprises approx. 1/3rd of all mature CD3 + T cells.
These are ‘restricted’ to the recognition of p MHC I complexes.
Also known as –
A) Cytotoxic T ( Tc) – identification of cells infected with
intracellular organisms, viruses and
bacteria and eliminate such cells.B) Suppressor T ( Ts ) – Down regulation of immune response.
NATURAL KILLER CELLS
Large lymphocytes ( 5 – 10% of peripheral blood lymphocytes ) which develop in the bone marrow.
They have an ability to kill virally infected cells and tumor cells without prior sensitization ( no need for antigen recognition)
Receptors - KARs and KIRs
γδ T cell
Cell which do not undergo positive and negative selection.
But expresses the TCR and CD3 but lacks the CD4 or CD8
γδT cells are thought to be a transitional cell type that may represent a bridge between the innate and adaptive immune systems.
γδ T migrate preferentially to the respiratory organs, the skin, and the peritoneal cavity.
They respond more quickly than do αβ T cells, but they do so without generating memory cells
T CELL ACTIVATION
CD 4+ T cell
APC = e.g., Macrophage
CD4MHCClass II
PeptideAntigen
TCR
1st signal.Formation of pMHC: TCR: CD
2ND signal.CostimulatoryMolecules.
+
1
2
CD 8 + T CELL MATURATION
p MHC CLASS I: TCR: CD8 +( 1st signal) expression of IL – 2 receptors
IL – 2 secretion by primed CD4+
( 2nd signal)
cytotoxic T Lymphocytes
cell lysis ( by perforin and
granzymes)