Re: What would happen if there was no immune system?

Jonathan,

The immune system has many different components.  Certain parts of the 
immune system are important in the IMMEDIATE response to a bacteria or virus.
Although this response is quick, the attack is a general strategy for any 
threat and is not specific for a certain bacteria or virus.  This initial 
response is called innate immunity.  Another major part of the immune system 
takes longer to respond to a bacteria or virus, but this response is very specific
in its recognition and attack against the invading bacteria or virus.  This is 
called specific (adaptive) immunity.  These two major arms of the immune system 
work together to destroy bacteria, viruses, and other threats to the immune 
system and host.  

Because of this structure of the immune system, there are no examples of a
person (or an animal) with the complete absence of an immune system.  HOWEVER, 
there are MANY examples of humans (and animals, such as mice which are often used
for research) who lack certain components of the immune system.  The general term
for an organism which does not have an intact immune system is to say that 
organism has immune deficiency.  

Generally speaking, an organism with an immune deficiency has some difficulty 
responding to infection.  The severity of this problem depends on the nature 
of the deficiency, however.  For example, there was a girl born without one 
specific kind of immune system cells called Natural Killer (NK) cells.  
For some reason, this girl is especially susceptible to infection by a certain 
group of viruses.

Despite the number of immune deficiencies that are found in nature, there is one
immune deficiency that is especially notable.  This immune deficiency is called
SCID and stands for Severe Combined ImmunoDeficiency Disorder.  There are 
a small number of humans born with SCID.  Generally these patients lack the cells
required for a specific immune response (which I mentioned previously).  These
patients are at EXTREME risk for infection and unless special measures are taken
these patients will often die during childhood.  One example of a SCID child
was the "Bubble Boy" who spent the majority of his childhood inside a bubble 
specially designed to be free of bacteria and viruses.  Without such special 
precautions a SCID patient CANNOT live in the normal environment.  
When looking on the web, I found the site of  a mother who has a child with SCID.
The effort that she has invested into this resource is worth your time to look at
if you are interested in further information about SCID and its complications.  

All the conditions I have mentioned so far have been conditions which people are 
born with.  There is another important group of immune deficiency, however, those immune 
deficiencies that are acquired during life.  There are two major groups in this
category:  HIV-positive AIDS patients, and people who are on immunosuppressive
medication.   

AIDS patients have immune deficiency as a result of the HIV 
infection, which debilitates a critical cell population in the specific immune
response.  AIDS patients often contract diseases not found in the normal 
population.  Such infections are described as "opportunistic infections" since 
they are generally considered minor threats to a person with an intact immune
system.  As is obvious from AIDS patients, the absence of a fully functional 
immune system leads to opportunistic infections as well as the inability to 
clear infections which are usually cleared by a person with an intact immune
system.  An important note here, is that AIDS patients do not die of HIV 
infection, but of a secondary infection which occurs because the patient is 
immune deficient (due to HIV infection).   

A second group of people who acquire immune deficiency, are people who are put on
medications to suppress their immune system.  These people are typically organ 
transplant recipients.  Without the drug to suppress their immune systetm, the 
person would often reject (destroy) the organ they received in surgery.  
With the drug, the organ can remain functional in the person for a much longer 
time.  Obviously, doctors must be careful to prescribe the right amount of drug.
Too much and the patient would be too susceptible to infection.  Too little and 
the patient would destroy their transplant.  Even with the right amount of immune 
suppressive drug, a person has an increased susceptibility to disease.  An 
important note for this group of people is that once they are taken off of the 
drug, they re-establish a normal immune system and can fully fight off infection.

As you can see, our immune system is very important in our everyday survival.
Without it we simply cannot fight off infection.  Although people always assumed 
this to be the case, the AIDS epidemic has been a tragic reminder of just how 
important a fully functional immune system is for our survival. 

Hope that helps.

ETC