Innate Immunity: The Natural Killer Cells

00:01 Let's look at the natural killer cell.

00:03 The previous talk, I again, like in these to a deranged person with an AK-47.

00:09 If natural killer cells don't see an appropriate self-antigen, a friendly face, they will fire.

00:18 So, why do we have NK cells? Well, they are important for immunity to intracellular pathogens.

00:27 And we have an example here of a virus infected cell at the bottom that is no longer expressing inhibitory receptors.

00:37 The loss of those inhibitory receptors, because of the viral infection will cause the natural killer cell to sidle up next to that cell and to kill it.

00:45 Natural killer cells also have on their surface Fc receptors.

00:48 So they recognize the constant fret constant region fragment of bound antibody.

00:55 And so, if antibody is bound to a particular target, they will come up bind with their Fc receptors and kill, this is called antibody-dependent cell mediated cytotoxicity or ADCC as you see on the screen there, They kill just like a cytotoxic T cell.

01:11 So they have within them preformed granules that contain porphyrin, which is a pore-forming protein, and granzymes, which will activate the intrinsic apoptosis pathways.

01:24 So when they form their synapse, when they bind, either through Fc receptor and an antibody recognition, or through that loss of the inhibitory receptors.

01:34 They will release porphyrin in a directorial fashion, punch a hole, and then granzyme will go across and will cause the death of the target cell.

01:45 That natural killer cells also make cytokines.

01:50 So they are going to be important for driving the stimulation of other cells.

01:55 This is all kind of trying to recruit a big inflammatory army that can deal with potential infections.

02:01 So here we see a macrophage talking to an NK cell, the macrophage is going to make Interleukin-12 that's IL-12, that will activate the NK cell and make it a more robust responding cell.

02:14 At the same time, that NK cell is going to make interferon gamma which will drive the activation of the interferon gamma macrophages and make them better at their job.