CELL MEDIATED IMMUNITY
Cell – Mediated Immunity
-
T Lymphocytes are involved in cell mediated immunity.
- They are produced in the bone
marrow.
- They attain functional maturity in
‘Thymus’ under the influence of a hormone called
‘Thymopoietin” secreted from
Thymus.
- They are 4 types of ‘T’ cells.
a) T helper cells (CD 4)
b) T Killer/Cytotoxic T
Cells (CD 8)
c) T Suppressor cells.
d) T memory cells.
a) Activation of T Helper cells:
Antigen binds to MHC class II protein on the surface
of Macrophage (Antigen presenting cell)
Forms a complex
secretion
of IL-1
Presentation to “T” cell “
Activation of “T” Helper cells
B) Activation of cytotoxic
‘T’ Cells:
i)
Antigen
in virus infected cells, cancer cells & foreign grafts.
Processing of antigen to peptide fragments
Peptide fragments of processed antigen bind
to MHC class I protein & forms a complex.
Presented to cytotoxic ‘T’ cells.
Activation of cytotoxic ‘T’ Cells.
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ii)
Another way of activation of
cytotoxic ‘T’ Cells
Antigen + MHC class II protein on the surface of macrophages (APC)
Interleukin – 1
Activation of ‘T’ helper cells.
Production of IL-2 by ‘T’ helper cells.
Activation of cytotoxic ‘T’ cells.
Function of Activated cytotoxic ‘T” Cells;
Activated cytotoxic ‘T’ Cells
Perforin lymphotoxin
Forms holes in the Activates
damaging
Plasma membrane of enzymes in the target cell
Target cells - Entry of ECF-
Swelling & burst of cell Destruction
of DNA
Cell
death
Cell death
Examples: Death of virus infected cells, Tumour
cells & foreign graft cells.
a) Function
of ‘T’ helper cells:
Take place
in both humoral & cell mediated immunity
i) Role in humoral immunity:
T- helper cells(TH2)
Interleukin – 2,4,5 & 6 (cytokines)
Activation of B Cells
Plasma cell
Secretion of antibodies
(ii) Role in cell-mediated immunity:
T- helper cells (TH1)
Interleukin – 2
Activation of cytotoxic ‘T’ Cells
Release of perferins & lymphotoxins
Death of target cells
b) Function of cytotoxic ‘T’ Cells:
- Destruction of Virus infected
cells.
- Destruction of cancer cells.
- Rejection of foreign grafts.
- Major defence against viral,
fungal & bacterial infection.
c) Functions of ‘T’ Suppressor cells:
- Suppress the production of
antibodies against the own tissue.
- this prevents the auto immune
diseases like Rheumatoid arthritis etc.
d) Function of ‘T’ Memory cell:
- Facilitates the activation of ‘T’
lymphocytes faster during secondary response.
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