CELL MEDIATED IMMUNITY (T-CELLS)

Chemoattraction is in response to:
a) Bacterial componants, eg. HAg, LPS, endotoxin, and
n-formyl met/leu/phe peptide (nfmetleuphe). The n-formyl group is only in bacteria, not humans.
b) Chemokines (4 types, based on structure)
1. cxc (eg IL8 = Interleukin 8)
2. cc (eg Rantes)
3. cx3c
4. c
c = cystene, x = variable amino acid
Two strategies of phagocytes:
1) Seek and destroy (PMN’s and macrophages)
2) Ag presentation (dendritic and macrophages)
NOTE: IgG = Secondary Immune response
IgA = Secretory
IgM = Primary response; default class
HOW ANTIBODIES ARE DERIVED

Pleuripotent Stem Cell--> Stem Cell --> Myeloid or Lymphoid:
Myleoid --> Granulocyte, Monocyte, or Dendritic cells
Lymphoid --> B Lymphoblast or T Lymphoblast
B Lymphoblast -->VDJ gene reassortmant =
CLONAL EXPRESSION --> B or T Lymphocyte
B Lymphocyte +Ag stimulation and T cell signal-->
CLONAL SELECTION (produces specific Ab by selection of VJD and CH class switching) --> CLONAL EXPANSION -->
either Plasma cell which secretes Ab, or Memory cell.

 Affinity maturation

ANTIGEN PRESENTATION
T Lymphoblasts --> CD 4+ and CD 8+ markers ->Naive T cell (Tho)
Tho (CD8+, CD4-) -->
MHC-I (Major histocomapatability complex 1) = Self Ag -->
CD8+ Cytotoxic T cells (kills host cells directly)
Why Kill Host Cells?
1) Host cell is infected with unkillable bacteria
2) Host cell has become cancerous, or dangerous

Tho (CD8-, CD4+) --> MHC-II (Foreign Ag)
CD4+ Helper T cells--> signal transduction --> cytokines with immunopolarization, two types of responses to optimize the response to the antigen:
Hallmark Cytokines of Type I Response:
1) Interferon gamma
2) Interleukin 12
Hallmark Cytokines of Type II Response:
1) Interleukins 4, 13

CYTOKINES / IFnγ IL-12 / IL-4, IL-13
EFFECTORS / Phagocytes, mostly / Antibodies
(mostly)
PARADIGM / CMI, mostly / Humoral
(mostly)
CLASS SWITCHING,
Affinity Maturation / IgG 1,3
(for opsonizing Ag
by gamma receptor) / IgG 2,4
(for Classical C’)

TYPE I Immunity TYPE II Immunity

(DEFAULT MODE)
Weapons to kill bacteria:
1) Complement
2) Phagocytes (self-armed, guided by signals= chemokines, IL, IFn gamma, mannose, etc.
NOTE: T cells affect phagocytes and humoral immunity because they provide necessary signals.
Staphylococcus aureus= pyogenic/purulent (much pus formed) This bacteria is handled by phagocytes = Type I immunity
Type II immunity: Some strains of S. auereus make a lot of catalase, which deactivates the H2O2 of phagocytes, so macrophages--> superkiller macrophages (which have much more toxic oxidative products).
Both Types I and II are necessary for S. aureus.
Mycobacterium tuberculosis
Prevents granule fusion to phagosomes by coating the inside of the phagosome so that toxic products cannot fuse there.
But the Ag on the surface can tell CD8+ cell to kill the host cell.

This is Type I response: antibodies are useless here.

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