InImm Revision

I believe some of us are still confused about what exactly is intracellular, extracellular bacteria. So here's my 2 cents worth.

OVERVIEW

1. Bacteria/toxin/viruses attach on the surface of a macrophage.
2. Taken into macrophage via endocytosis.
3. Vesicle is formed inside the macrophage. (another name for vesicle is phagosome)
4. If the phago-lysosome fusion is able to take place, bacteria is called a EXTRACELLULAR bacteria. If the fusion is unable to take place, bacteria is called an INTRACELLULAR bacteria. If the virus manage to penetrate the vesicle to enter into the cytoplasm without the fusion process, it is a FREE-FLOATING CYTOPLASM.

INTRACELLULAR BACTERIA (Example: TB)

How our immune system is evoked.

1. Endocytosis of bacteria cell into macrophage.
2. Fusion of vesicle and lysosome is triggered.
3. As the fusion is prevented, IL-12 is released by macrophage.
4. Antigens are processed and presented as MHC Class 2.
5. APC cell talks to a CD4+ T cell.
6. IL-12 released by macrophage stimulate CD4+ to differentiate into TH1 t cells.
7. Activated TH1 cell activates macrophage, makes it more aggressive, forces fusion to occur.
8. Once fusion has occured and downstream processes is carried out, IL-4 is released by macrophage.
9. IL-4 activates TH0 T cell into TH2 T cell.
10. TH2 T cell activates B cell, makes them proliferate and produce antibodies.
11. Antiobodies will target those intracellular bacteria present outside the cell. (read up on functions of Antibodies)

EXTRACELLULAR BACTERIA
Example: bacteria toxin

How our immune system is evoked.

1. Endocytosis of bacteria cell into macrophage.
2. Fusion of vesicle and lysosome is triggered.
3. After digestion of bacteria, IL-4 is released by macrophage.
4. Antigens are processed and presented on MHC Class 2.
5. APC cell talks to a CD4+ T cell.
6. IL-4 released by macrophage stimulates TH0 into TH2 T cells.
7. TH2 T cell activates B cell, makes them proliferate and produce antibodies.
8. Antiobodies will target those intracellular bacteria present outside the cell. (read up on functions of Antibodies)

FREE FLOATING IN CYTOPLASM
Example: viruses

How our immune system is evoked.

1. Endocytosis of bacteria cell into macrophage.
2. Viruses manage to penetrate through vesicle and enters cytoplasm.
3. Antigens are processed and presented as MHC Class 1 molecules.
4. APC cell talks to CD8+ T cell.
5. CD8+ T cell is activated and lyse cell via perforins or FasL.

Best of luck!

Carine