1. ComplementSystem

2. Phagocytes (neutrophils, macrophages, mast cells)

INNATE IMMUNE SYSTEM

ADAPTIVE IMMUNE SYSTEM

Lymphocytes: T and B Cells

cells of innate immunity

Cells of adaptive immunity.

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

T LYMPHOCYTES- CELL MEDIATED

IMMUNITY.

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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

THYMOCYTE DEVELOPMENT: +VE/-VE SELECTION

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 4 + CELL MATURATION.

TH 1

TH 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)