Changes

==NK Receptors==

==NK Receptors==

* Some viruses down-regulate MHC expression of the infected cell

Some viruses are able to down-regulate MHC expression of the infected cell; this mecganism is also used as a protection against the host immune system as a lack of MHC inhibits normal T-cell activity. NK cells can counteract the down-regulation tactic and in this regard are mainly associated with activity against virus-infected cells and tumour cells, which can also have lowered MHC expression.

** This is used as a protection against the host immune system

 

*** Lack of MHC inhibits normal T-cell activity

The receptors on NK cells do not act like antigen-specific receptors because although they trigger functional activity within the cell, they do not stimulate proliferation and there is no clonal expansion of NK cells. NK cells work through two different types of receptors:

* NK cells can counteract the down-regulation tactic

#'''Activating receptors, R1''' which recognise pathogen-associated glycolipids or Fc receptors (E.g. CD16 recognises Ig that is bound to pathogen antigens)

** They are mainly associated with activity against virus-infected cells and tumour cells, which can also have lowered MHC expression

#'''Suppressing receptors, R2''' which recognise target cell MHC molecules.

* The receptors on NK cells '''do not''' act like antigen-specific receptors

When an NK cell interacts with a target cell it will be activated via R1 - if the target cell expresses MHC this will be seen by R2. R2 suppresses the activities of NK cells.

** Although they trigger functional activity of the cell, they do not stimulate proliferation

 

*** There is no clonal expansion of NK cells

If the target cell does not express MHC, the suppressing receptors are not engaged; the engagement of R1 therefore causes activation of the NK cells

* NK cells work through two different types of receptors

 

** '''Activating receptors, R1'''

*** Recognise pathogen-associated glycolipids or Fc receptors  

**** E.g. CD16 recognises Ig that is bound to pathogen antigens

** '''Suppressing receptors, R2'''

*** Recognise target cell MHC molecules

* When an NK cell interacts with a target cell it will be activated via R1

** If the target cell expresses MHC this will be seen by R2

*** R2 suppresses the activities of the NK cells

** If the target cell does not express MHC, the suppressing receptors are not engaged

**** The engagement of R1 therefore causes activation of the NK cells

[[Category:Lymphocytes|G]]

[[Category:Lymphocytes|G]]