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Suppose that a person has the ability to kill any living being it touches (literally). That happens due to the fact that when this person touches using such ability, the target's spot being touched starts to become necrosis/gangrene and spreads to the whole body in seconds, and finally causing the death of the touched one.

This person's hand has no visible anomalies and the necrosis on touch only happens voluntarily, i.e., touching normally or someone touching this person has no effect.

With that, what would be the possible implications? What would be necessary so that this necrosis/gangrene results in death, and so fast, and allowing to control when it functions or not?

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  • $\begingroup$ Implications of a person with this ability? Once this gets known, he would get locked in a max security cell and anybody visiting him has to wear a bio-hazard suit. $\endgroup$ – Skye Sep 14 '16 at 12:31
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You could trigger Apoptosis. You can trigger it by chemical signals external to the cell, triggering "cell suicide".

Apoptosis triggered by external signals: the extrinsic or death receptor pathway

  • Fas and the TNF receptor are integral membrane proteins with their receptor domains exposed at the surface of the cell
  • binding of the complementary death activator (FasL and TNF respectively) transmits a signal to the cytoplasm that leads to activation of caspase 8
  • caspase 8 (like caspase 9) initiates a cascade of caspase activation leading to
  • phagocytosis of the cell.

Example (image): When cytotoxic T cells recognize (bind to) their target, - they produce more FasL at their surface. - This binds with the Fas on the surface of the target cell leading to its death by apoptosis.

The early steps in apoptosis are reversible — at least in C. elegans. In some cases, final destruction of the cell is guaranteed only with its engulfment by a phagocyte.

enter image description here

Source: Apoptosis at Kimball's Biology Pages. Wikipedia links added for reference.

The process naturally stars by the presence of FasL - It should be possible to accelerate it by exposing the subject to an large dose of the Death-inducing signaling complex.


Behavior

The person would die before the cell destruction of the body is complete. Apoptosis causes cell death in an orderly fashion, the dead cells break in pieces and the parts get engulfed by phagocytes. Basically the body is eating its own tissue.

Starting from the surface it would make an open wound in the skin, muscle, and veins... that should cause bleeding. Of course red cells are being eaten too. Once the process reaches the internal organs it should cause trigger systemic failure and death.

If the resources to sustain this process are being given by the attacker - perhaps even the phagocytes - it could be as fast as needed to be.

Control

Controlling it is another subject... my suggestion would be to encapsulate the biochemical agents in small membranes that would open on contact with the target tissue. Then it could be released similar to spores.

Appearance

On the first stage It would go red first and skip the inflammation of early necrosis - unless you caspases for inflammation, and would you? - So, it would look as if it were a skin burn.

Once it peels off the skin it would look more like necrosis. Yet, I would expect that it would be mostly yellow for the reasons explained below.

In the case of gangrenous necrosis, the blood supply to the area has been cut out and the cells are dying. Due to the lack circulation, macrophages that would usually eat the dead cells can't reach the area. For uncontrolled apoptosis the blood supply to the area is still intact – except on the spot, once veins are being eaten, it is bleeding - and so dead cells wont accumulate, at least not until the phagocytes has reached saturation.

Also note that if the attacker is covering the target with the biochemical agent that causes this, the appearance of the process would be affected by the appearance of that agent. That is, if you want it to look black, make the agent black.

Note: I could not find examples of uncontrolled apoptosis on the sking that were not accompanied by skin cancer.

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  • $\begingroup$ What would be the appearance of this? A hole expanding and killing all cells around the spot, or similar to necrosis' black/yellow? $\endgroup$ – Yuuza Sep 14 '16 at 19:46
  • $\begingroup$ "A hole expanding and killing all cells around the spot" that's the idea. Updated answer. $\endgroup$ – Theraot Sep 15 '16 at 2:16
  • $\begingroup$ Use that as the basis for a toxin, but look at tge stingging cells of a jelkyfish for delivery! $\endgroup$ – JDługosz Sep 16 '16 at 5:53
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Clearly you need a toxin which can exploit existing apotosis pathways in the cell, as elaborated by Theraot’s answer. But I think it would be based on nanotechnology and act more in the way of an active pathogen, going around and injecting individual cells and spreading more of itself: a virus, IOW.

The delivery mechanism is what I want to contribute. I’m reminded of how jellyfish use stinging cells calledcnidocytes which are really nasty: a long tube is coiled in the cell and it explosivly deploys by turning inside out like a sock being removed, going through the protective outer skin and into underlying tissue and hopefully hitting capilaries. Along its entire length it releases the toxic agent as it goes, like an ever-growing needle.

picture

Unlike the jellyfish, these can be under protective covers so they only are discharged by first pulling the pores open and willing them to be primee.

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Answer: Palms with Controllable Porosity and a Subcutaneous Poison Reserve

The biggest problem you have is that you don't want to poison someone then immediately die after scratching your ear. In fact, with the Reality Check flag in play, I'm going to point out that's pretty much what would necessarily occur. After all, if your SKIN passes a chemical to other SKIN which causes SKIN to decay and die... well, your SKIN would be exposed to the chemical first and you would both die.

But it's more fun to make up a "what if" scenarios that bend that tag a little bit...

Hand Construction

Firstly then, you need a way to deliver your poison via touch without constantly oozing it or dying immediately yourself. The best answer I could give would be that some part of your hand is not, in fact, covered in skin but in some other sheathing material (which may or may not LOOK like skin). Let's say you had a patch with an inorganic callus, as an example. You would then also need a subcutaneous reserve of poison (also lined in something immune to the poison) and an active muscle that could pull at your inorganic callus to open it up. At that point, by flexing your "poison muscle" and pushing your callus into someone else's skin you would push some of your poison through the pores in the callus and onto their skin, killing them.

The next issue you would have is that you do have some instant-death poison on your hand, albeit not touching your skin yet. The only answers I could provide would be to suggest that either the poison oxidizes quickly (the oxide being non-toxic as a topical poison), or it evaporates. If the poison is organic, perhaps it dies quickly without something to feed on. I think the oxidizing method is more likely to work out, but given that I think we already fail the Reality Check flag I'm not too concerned about it.

Poison

Again failing the Reality Check flag, there is no known substance that would do what you are looking for. There is nothing even close.

As a stand-in, what I would propose that the closest analogue would be that the poison you excrete is actually a fast-replicating virus that probably uses apoptosis as suggested by Theraot. I'm pretty sure that if we were worried about reality the person would still have at least many hours to live, but their death could be as horrible as you describe.

The virus could also be engineered to hibernate unless it is in the presence of oxygen (which is not present in the lining of your poison sac), at which point it must feed or die quickly. That would explain why it kills others and why, after some period of time, it doesn't kill you when you scratch your ear later.

Or you could just claim it's a chemical that triggers a waterfall effect of cell death and not try to explain the mechanism. After all, we have already given up the Reality Check portion of the answer.

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    $\begingroup$ One thing -- our bodies have pretty darn good mechanisms for recognizing "self" vs "not self" built right in -- why not key off those? $\endgroup$ – Shalvenay Sep 16 '16 at 23:36
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One idea would be to have someone who has the ability to, on command, secrete a fluid rich in Natural Killer (NK) cells, along with some nutrients for them to run on, from his palms (perhaps by modifying sweat glands). Normally, NK cells are a part of the human innate immune response, and respond to any cell that does not express a proper set of "self" markers, or no "self" markers at all, by telling it to commit cell suicide, i.e. apoptosis, or by directly lysing the cell instead.

Furthermore, his NK cells would be modified so that a NK-specific retrovirus is expressed by them, its replication suppressed by "self" MHC antigens being presented to the NK cell, with the retrovirus controlling what "self" is. The result is that once the modified NKs come in contact with a "not self", they start the apoptosis process on the "not self" cells and also emit retroviral particles, which attack the NK cells of the victim and make them stop recognizing the victim as "self", creating a chain autoimmune reaction which necrotizes the victim from the inside out.

You could also expand on this by making it so that the modified NK cells also express a large quantity of apoptosis factors when "self" is no longer presented to them, but this may not be necessary depending on how fast and hard you wish this to work. (Phagocytes can also be added here, of course, with their behavior controlled by factors emitted by the NK cells.)

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  • $\begingroup$ I think this answer could be a lot better (and the ideas more widely appreciated) if it was easier to understand by the non-expert. On my first reading I didn't know whether you were referring to real things or introducing madetup ideas—there was no explaination, introduction, or links. I added links to some important terms. … $\endgroup$ – JDługosz Sep 17 '16 at 7:44
  • $\begingroup$ I would suggest breaking it after the first sentence, then inserting “NK cells are…” and explaining the idea of what happens naturally. Then say you will engineer that this mechanism should be turned against the body and then go into how. Also introduce the further refinement of spreading the changes to NK virually. The second paragraph is too technical to follow an probably doesn’t add much. $\endgroup$ – JDługosz Sep 17 '16 at 7:48
  • $\begingroup$ The average reader will be more interested to learn about the body’s mechanisms for this, and not care as to the exact molecule names. For most widespread interest, focus on explaining the mechanism that exists. $\endgroup$ – JDługosz Sep 17 '16 at 7:50
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Poison

Some venom cause necrosis when injected.

Your person had venom gland linked to an invisible way to inject it, like a cnidocyte, all over his hand, that can produce venom on command. This venom kill cells quickly, occasioning necrosis.

Once the hand touch someone, the venom pass trough skin and diffuses on the whole body via blood vessels, which causes the necrosis to spread.

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