their are sites in which pathogens can resiad, extracellularly & intracelluarly
E.g., extracellularly
- Streptococcus pneumoniae
- Pneumocystis carinni
- Trypanosoma brucei
E.g., intracelluarly
- Viruses
- Mycobacterium tuberculosis
- plasmodium falciparum
the immune system deals with pathogens that exist intracullarly in different ways from those that exist extracullarly
How dose the immune system deals with these different types of pathogenes
A- Extraceullar pathgoenes
antibodies are the primary defense aginst extracullar pathognes by different ways
= Nutralization =
so for example a bacterial toxins bound to a cell, so if we have an antibody against that bacterial toxins , the antibody will bind to the toxins & block its action resulting in nutraliztion
= Opsonization =
antibody on the surface of extraceullar bacteria can bind to Fc receptor on phagocytic cells & taking mor effectively by phagocytic cells
= complement activation =
activation of complement can result in lysis
B-Intraceullar pathogens
Once the pathognes inside the cells the antibody will not be effective. so it has there another way to deal with these pathogens & this by cell-meidated immunity
pathogenes inside the cells can exist in one of two places
they can exist in the cytosol for example the viruses & some bacteria , the other side where the pathogens can exist in the vesicles for example some bactria & parasites & the way in which the immune systme deals with these two different types of intracullar pathogens is different
in the case of pathogens into the cytosol, the response is mediated by group of cells called cytotoxic T cells (CD8) cells
* if we have a virus that infect a cell & its going into the cytoplasm of the cells & as its replicated there is some of viral-protien that will present on the surface of the cells & then the cytotxic will recognize these & kill the cells
in case of the intraceullar pathogens in vesicles, the response is different , here the immunity is mediated by different T cells, the helper T cells & whats heapning in this case (for example in mycobacterium tuberculosis) & whats happened that when the cells harpor these pathognes for example when tuberculosis infects the macrophages the bacterium inhibits phagolysome fusion that making the macrophages unable to kill the bacteria
as some of the antigne express some of bacteria antigen the T helper cells its get activated & it secretes a series of cytokines & then those cytokines (mostly interferon gamma) the macrophages get activated, now the lysome infuse & kill the bacteria
So into the cytosol it will be a cytotoxic response & in the vesicles it will be a helper response
Notes
When we get infected by a pathogens we can run both the antibody & cell-mediated immunity for example in cases of viruses , once the virus enter the cells we need the cytotoxic cells to kill the virus but that dose not mean that antibody dose not have a role , they are very important in subsequent exposure
