Human Immune System

[Clockwork]

So, science people among us, would you indulge me in a little lot of ignorance mixed with an equal amount of curiosity? I hope so otherwise this will just be another dead topic I've started.

I asked myself if humans had the best immune system of all creatures on this planet. I thought at first, probably not - elephants and whales might have stronger immune systems due to the general big is better rule guideline (live longer, smarter etc...and yes humans are an anomaly to this as they are to so many other things). I attributed never having seen a sick animal down to me rarely seeing them apart from on tv. I have searched but from what I can tell there isn't really very much information or many studies done on elephant immune systems. I would assume then that disease isn't a major killer among them otherwise there would be more studies done. Also: being bigger and having larger organs; they could withstand more of an infection, giving the immune system more time to respond (big guess right here).

Then I considered insects, having an exoskeleton would make them less likely to acquire a pathogen surely? The skeletal structure wouldn't be porous enough to allow much (if anything) though. Reading this http://www.scientificamerican.com/article/what-kind-of-illnesses-do/ told me otherwise but it does mention that they have extremely effective immune systems.

The answer (apparently) is the first line in this report http://www.jacksonfreepress.com/news/2012/nov/05/research-funding-takes-hit-usm/, though I'm not sure of the validity of it.

So apparently humans do have the best immune systems. I then asked myself why that was, and as always my first instinct was to say: it's just evolution. Upon further thought I tried to ascertain why we would have evolved that way. Firstly, we have porous skin. It keeps us cool and properly hydrated (and feels great ) but also isn't as good as an exoskeleton, scales, leathery hide, fur (though that carries another risk) at keeping out pathogens.

Although being a wolfman I am an anomaly to this, humans are losing their body hair as an evolutionary process. We started off with less than monkeys but more than Brian Blessed and have been losing it since we decided to stop being naked all the time (yes, that's why geordies are growing it back). I would assume, then, that while the least complex pathogens were evolving and infecting us our immune systems grew at a faster pace than other creatures due to our sociability (another huge guess. More sociability=more people get the disease which leads to more potential survivors to pass on immunity?).

After that there was one link I hadn't really looked at: the pathogen itself. I'm using the broad description of any disease causing microorganism not because it's right or necessarily because that's even what I mean by it but because I know too little about each type to use them correctly. This is where my knowledge is especially sketchy and is more guesswork than anything.

Guess one: pathogens require another thing to exist which is why they are not (until further classification) technically living.
Guess two: pathogens 'like' energy. Energy in this sense is from heat from the host which is why humans are a better species for the pathogens to evolve to infect than, say, reptiles or fish.
Guess three: pathogens have been trying to evolve to infect humans (being the ideal host for pathogens) for so long that they have 'forgotten' to evolve to infect anything else which is why there are so many more diseases that affect humans than animals. That is also a guess.

So anyway I'm not too impressed with how little I know on the subject or on how vague and possibly incoherent my thoughts are.

If anyone can tell me anything about this, that would be great. Or if someone could just say they read it and it sort of made sense...anything. xD

[comrade_general]

I thought we had more hair than other apes? A lot more, ours is just finer and more condensed in areas while theirs is coarser and more evenly distributed.

[Clockwork]

I don't know actually. In terms of percentage of body coverage I meant.

[Silver Wolf]

Although being a wolfman I am an anomaly to this, humans are losing their body hair as an evolutionary process.

And what am I then?


Saying that humans have the best immune system is just a bunch of nonsense if you ask me.
Sure our immune system is able to cope with a wide range of various pathogens, but the development of medicine is the main cause why our immune systems work so well.
Just a few hundred years ago people were dying of common cold and various secondary infections that are easily treatable with antibiotics. Not to mention the outbreaks of plague.
And the fact is that our hygienic standards are much higher, so we keep the amount of various microorganism relatively low in our environment. Animals don't have that luxury.
We also control our environment how we please. That's a huge factor to consider.

Guess one: pathogens require another thing to exist which is why they are not (until further classification) technically living.

Not necessarily.
Viruses, for example are always classified as something between living (they carry genetic material, reproduce, evolve) and non-living (they lack cell structures). Here you may be right.

But looking at bacteria, like E.coli for example, you're wrong. Essentially a beneficent inhabitant of our intestines (produces vitamin K₂, prevents other bacteria from settling in), but some variations can cause serious food poisoning. There are many other similar examples, but this one is the most common. Obligate pathogens are not the only kind of pathogens, as you know.
Bacillus anthracis, which causes anthrax usually inhabits the soil (and in relatively huge quantities, if I remember correctly).

Parasites should also be included here... Even though they are not microorganisms they still make your immune system go wild. Consider Trichinella spiralis and it's life cycle as an example... The main reason why it's eggs remain incrusted in human muscles is because our immune system tries to neutralize the threat (unsuccessfully, though).

Guess two: pathogens 'like' energy. Energy in this sense is from heat from the host which is why humans are a better species for the pathogens to evolve to infect than, say, reptiles or fish.

Not entirely true.
I've had an aquarium for a number of years and I can tell you that fishes do get sick a lot.
It's just that fishes are usually more prone to fungal infections and parasites. Bacterial infections like fin rot are still present, though.

I don't know much about the reptiles unfortunately.

Guess three: pathogens have been trying to evolve to infect humans (being the ideal host for pathogens) for so long that they have 'forgotten' to evolve to infect anything else which is why there are so many more diseases that affect humans than animals. That is also a guess.

Incorrect. Consult this wonderful chart:

Spoiler (click to show/hide)

You'll see that birds carry the most types of influenza. Which is completely understandable when you consider the way chicken are breeded now-days. Huge populations in crowded spaces, artificial lights, non-balanced diet and so on... All of that has impact on their immune systems and makes the job easier for pathogens.

And then there are pigs.
Also one of the most common farm animals and the most dangerous vector (judging from the human perspective) for various strands of the disease.
Probably due to similarity of our immune systems.

So anyway I'm not too impressed with how little I know on the subject or on how vague and possibly incoherent my thoughts are.

Same here. I'm feeling a bit stupid being a third-year student of biology...

[Clockwork]

Nice one, thank you so much for taking the time! I learned a lot reading your responses

I've never studied any of this (did a bit for GCSE I guess) so my terminology is horrible. I think what I meant was viruses across the whole thing.

When I was looking for stuff on this online, it was pretty unhelpful...Or I'm lousy at searching.

The wolfman thing is because I'm ridiculously hairy and have slightly elongated nose and canine teeth

[comrade_general]

[Silver Wolf]

It's a valid question, really.
And a lot of stuff can be said about it, but saying, quoting: "humans have the best immune systems on Earth" as they did in the article, without any explanation how or why is just wrong. It may be true in some aspects, but those aspects must be precisely defined and backed up by proper scientific facts.

And there are many exceptions when it comes to immune system and pathogen tolerance.

Take Africa, for example.
Malaria is a common disease, especially in the southern half of Africa.
The population there (black people) usually shrugs it off very easily.
The question is why?
The thing is, black people are prone to a hereditary blood disorder, Sickle-cell disease (SCD), or sickle-cell anaemia (SCA).
This disease makes red blood cells (erythrocytes) stick together because their abnormal hemoglobin (named HbS).
Now this only happens if you're unfortunate enough to be a homo-zygote for that trait (carrying two sickle-cell genes). And that usually means that you'll die before reaching 30 due to circulation problems.
On the other hand, carrying a single sickle-cell gene (sickle cell trait) means that you won't get any of these symptoms. Your children might, if you have them with someone who also carries that single gene.
However, that single sickle-cell gene makes you immune to most of the lethal types of malaria...

The point is, very small changes and interactions at the molecular level (just one different base in the nucleotide sequence of the hemoglobin molecule in this example) make HUGE differences.

[Clockwork]

That happens whenever I sneeze.

[Clockwork]

On the other hand, carrying a single sickle-cell gene (sickle cell trait) means that you won't get any of these symptoms. Your children might, if you have them with someone who also carries that single gene.
However, that single sickle-cell gene makes you immune to most of the lethal types of malaria...

The point is, very small changes and interactions at the molecular level (just one different base in the nucleotide sequence of the hemoglobin molecule in this example) make HUGE differences.

Yeah I saw this, isn't it when the disease and the genetic disorder have the same markers or something so the body is already fighting something that 'displays' the same?

[Silver Wolf]

Yeah I saw this, isn't it when the disease and the genetic disorder have the same markers or something so the body is already fighting something that 'displays' the same?

Yes, close enough. The thing is that the body is not fighting the disorder actively.
Tertiary structure of the defect hemoglobin (Hbs) is changed, so they eventually become distorted and are removed from circulation sooner, and the parasites within them are not able to finish their life cycles.
The fact is not all erythrocytes of the sick person have that shape. The numbers are around 50% for homozygous people. So they can still get sick, but the disease won't spread too much. However, their immune systems are a mess.
Heterozygous people do not have the same level of resistance, but it still present.

It is also possible that this disorder evolved as a genetic response to endemic malaria.

[Will]

It is also possible that this disorder evolved as a genetic response to endemic malaria.

Life expectancy of those with sickle cell anaemia is not so much different to the average historically. This means that generally there was not a lot of reason for people without the disease to be at an advantage since they were being killed off by other things anyway. However malaria is the biggest killer of mankind, and so resistance against it of course meant a greater chance to produce progeny and to pass on the gene.

The population there (black people) usually shrugs it off very easily.

If you look at the number of people that die in Africa from Malaria, I wouldn't say they shrug it off very easily. The number of people dying from it is now decreasing, but that is because of aid efforts.

[Silver Wolf]

If you look at the number of people that die in Africa from Malaria, I wouldn't say they shrug it off very easily. The number of people dying from it is now decreasing, but that is because of aid efforts.

I agree, "very easily" was a clumsy figure of speech.

But not all people in Africa carry that gene. That's one of the reasons.
Without the help of HgbS those numbers would be significantly higher.

[TTG4]

Silver Wolf has made most of the points I'd want to make here. I'm going to throw plants into the equation though.

Arguably, these guys have the 'best' immune systems in my opinion. I'm defining best here as protecting against many different pathogens trying to colonise you.

Firstly, they have increadibly tough cell walls, which make it difficult for anything to actually get into the cells. Even if they get past this, there are proteins on the surface of the cells which detect the pathogen and cause an immune response. They do this by recognising a protein which is the same among large amounts of potential pathogens, such as flagellin (a component of the bacterial flagella, which they swim with) or chitin (which makes up the fungal cell walls).

Now this is where it gets really awesome, these pathogens secrete proteins called effectors which prevent these immune responses. Since they have to evolve these independently, it means very few pathogens can colonise a single species effectively!

Though, the plants then develop proteins which detect these effectors and trigger an even stronger immune response, and so on and so on...

Anyway, back on topic, your point on sociability is definitely valid. The increased crowding and squalor in early cities is pretty much a pathogens dream!

[Clockwork]

Wow I did not know that about plants, sounds useful. Thanks

In the far future I can see we'll take that ability and graft it onto humans.

[Cuddly Khan]

So you're TTG4, *nods to self* still don't know you.