Cell Mediated Immunity II – Flashcards

CD8:Kill infected cells displaying foreign Ag, typically virus infected cells.

CD4 (TH1): Stimulate macrophages

to kill intracellular pathogens.

CD4 (TH2): Stimulate

antibody production to facilitate elimination of  extracellular pathogens.

Effects of Macrophages:

MHC Class II Increases

TNF Receptors Increase

Oxygen Radicals Increase

Nitric Oxide Increases 

These changes activate the macrophages to become highly microbicidal.  Important because so many pathogens can replicate in macrophage vessicles.

Activated by interferons – thought to act primarily during the early stage of infection, but can influence adaptive responses.

Inhibited by MHC Molecules

Stimulation of NK cells is not antigen specific – it is mediated by an ‘activation receptor’.

Interaction with any MHC molecule (not specific) inhibits the cytotoxic activity of NK cells.

Two reasons :

a.  prevents killing of host   

     cells, because they

     typically express MHC

b.  enables killing of cells

     that don’t express MHC

-some viruses downregulate MHC expression as a

       means to avoid detection by T cells

      Three phases :

1.  activation and expansion – 100 to 50,000-fold expansion

  2.  death (“AICD”) – 95% of cells die

  3.  memory (stability) – cells maintained at low frequency

Compared to primary responses, memory responses are :

  1.  Higher frequency of antigen-specific cells (~1000x)

  2.  Faster (due to changes in gene expression)

  3.  Develop effector cells more efficiently (ie, requires lower Ag doses)