Question

During a recent Ebola outbreak, researchers attempted extracting antibodies from people who had been infected but survived. They then injected other people with these antibodies to help them overcome the illness.   Even more recently, an experimental vaccine against Ebola has been approved for emergency use in the Democratic Republic of the Congo. Ebola is a virus that infects macrophages and dendritic cells. In doing so, it causes dysregulation in several ways. For example,

1) it prevents infected cells from secreting interferons,

2) it causes infected cells to secrete massive amounts of pro-inflammatory signals,

3) it allows infected cells to present antigen to Th cells, but causes the infected cells to encourage the Th cells to commit apoptosis.

4) Causes NK cells to commit apoptosis.

5) Finally, Ebola also causes endothelia to NOT express surface adhesion proteins (ex, selectins).

Explain the roles of interferons and of NK cells in fighting viruses.

Answer 1

Natural killer cells are large granular lymphocytes (LGL) developed inside bone marrow .

Also called Null cells as they do not have any surface markers that is No T cell receptors but antigens present CD16 and CD 56.

Natural killer cells is part of Innate immunity and secrete T cell like cytokines but have no receptor for T cell.

Nk cell have 2 recepor activating and Inhibiting receptor .Normal healthy cells have Expression oF Major histocompatibilty Complex MHC1 and activating ligand for activating receptor on NK cells .a

When NK cells come in contact with Healthy tissue no damage occur beacuse it bind the MHC with inhibiting receptor and signal is stopped there and further cascade doesn't occur .

In case of virus infected cells,MHC expression is almost lost so NK cells bind the activating ligand on virus infected cells with activating receptors and inflammatory cascade started with release of Interferon gamma which activate the macrophage and destroy the cells intracellularly as well .

Proliferation of NK cells is by Interlukin 2 and Interlukin 5

It is cytotoxic cells and destroy the cells by osmotic lysis or trigger apoptosis .

One more mechanism is there NK cells destroy the Antibody coated antigens by ADCC antibody dependent cell mediated cytotoxicity .Antibody FC portion bind with antigens and Fc receptor is present on NK cells CD16 which interact with each other and cause destruction of cells .

So in these ways NK cells kill virus ,cancer cells.

Interferons gamma source iS T cells

It cause macrophage activation

MHC class 1 and Class 2 expression on cells

Activates the Nk cells .