3. Hypersensitivity Type IV
General concept
Delayed type hypersensitivity (
takes 2 or 3 days to develop).
No antigen antibody mediated
response.
Cell mediated response.
4. Cells involved in Hypersensitivity
Type IV
T Lymphocytes : are further divided into
two types.
Helper T Cells (CD4)
Cytotoxic T Cells (CD8)
5. Antigen Recognition
T cell fail to recognize antigen in the
absence of Antigen presentation.
T cell receptor is restricted to recognize
antigenic peptide only when bound to the
appropriate molecule major histo
compatibility complex (MHC).
This is called MHC restriction.
6. Two Categories of Antigen
Are processed and presented to T cell
by two different mechanism.
Exogenous Antigen
Endogenous Antigen
7. Exogenous Antigen
Present MH class II.
Are taken by the Antigen presenting cells (Dendritic
cells ; Macrophages).
8. Antigen Presenting Cells:
Engulf the antigen by endocytosis.
Endosome fuses with the Lysosome.
So antigen is degraded into fragments.
Display on cell surface by combining with MHCII
Here they may be presented to CD4 helper T cells.
CD4 helper T cells then become activated.
9. Function of Activated CD4 (Helper
T cells)
Responsible for regulatory functions.
Produce interleukin
Interleukin 2 activates CD4 and CD8 also
called as T cell growth factor.
Interleukin 4 and 5 are activator of B cells.
Gamma Interferon activates macrophages;
NK cells; neutrophils.
11. Endogenous Antigen
Present MHC1 class.
Antigen present within the cell e.g, viral protein
in any infected cell are;
Degraded into peptide fragment.
Peptide fragment form a complex with MHC I.
Displayed at the cell surface.
Here they may recognize by CD8 ( Cytotoxic
Cell).
12. Function of Activated CD8 cell
Perforins: formation of channels
through the membrane.
Pore formation.
Cell content is lost.
Cell dies.
13. CD8 ( Cytotoxic T Cells)
Granzymes:
Proteases
Degrade protein in cell membrane loss
of cell content
Cell dies