Conclusion

In Answer to the Problem

Since the immune system has many parts that all play major roles in defending the human body, it is impossible to pinpoint a single cause behind why people who grow up in pathogen-free environments have weaker defences against autoimmune diseases and allergies than do those who grow up in pathogen-filled environments.

It is particularly interesting that this lack of immunocompetence affects only those who are exposed to different concentrations of pathogens in childhood, but not in adulthood. Future studies that could take a look at the ‘optimum saturation’ of pathogens for a human could have large influences on the ways that children will be raised in the future.

Through the research outlined here, however, many reasons can be postulated for this lack of immunocompetence of the adaptive immune system in people who, as children, were brought up in a sterile environment. These include a lack of activation of suppressor t-cells, an excess of genetic recombination for antigen-responses, a quicker defence carried out against the antigens that the body has primed itself against, i.e. those in itself, the presence of more professional APC’s, and the presence of more immune cells (as they have not yet been killed in combat).

Lack of Activation of Suppressor T-Cells

In the human body and immune system, suppressor T-cells perform the task of shutting down the immune system when the body has failed to distinguish self-cells from non-self cells, and effectively begins attacking itself. Suppressor T-cells do this using either cell-to-cell contact or through the release of TGF-Beta and Interleukin 10.

The trouble occurs when not enough Suppressor T-cells are activated by the body, due to a lack of actual attacks by pathogens. When the body is at first attacked, all other defence cells are found and activated in high numbers, except for the suppressor T-cells. These suppressor T-cells are not only found in lower concentrations, there are also fewer activated suppressor T cells. There are, however, enough to do their job when foreign pathogens attack the body.

Nonetheless, this has a negative impact on immunity. This immune system, filled with immature suppressor T-cells, is easily overwhelmed. Due to this, when there are two antigens recognized, there are only enough activated suppressor T-cells to fully shut down one response – the one that comes first.

However, if the second response is against a self-antigen, this response continues, and the body attacks itself. By the time the immature suppressor T-cells realize that the attack is against a self-antigen, the response is too far along, and there is an insufficient number of activated suppressor T-cells left due to the previous infection. Hence, the lack of activated suppressor T-cells may be the cause for the lack of immunocompetence in children that grew up in pathogen-free environments.

Too Much Genetic Recombination

The concept of genetic recombination is based on the fact that the body codes itself against any antigens it may encounter. Antigen stimulation may cause more antibodies to be coded against different antigens, but the majority of the antibodies the body produces are produced in childhood, through genetic recombination. It is not clear exactly when this process stops, or why.

The reason for the halting of genetic recombination may be that when the body launches an immune attack, the energy invested in the immune system goes elsewhere, and the process of genetic recombination is halted.

However, if the immune system does not encounter a foreign antigen for a long period of time (due to fewer pathogens being found in an environment), the process of genetic recombination may go on for a much longer period of time than was normally intended. This would cause the body to be coded against far more antigens – antigens that are likely to be found within the body itself.

Due to this increase in the types of antigens the body can produce antibodies against, it is far more likely that the body will find antigens within itself that it will attack. This will cause more autoimmune diseases and allergies for that human body.

A Quicker Defence Against Itself

The absence of other foreign pathogens that attack the immune system causes it to be primed against professional APC’s and antigens within itself in order to gain practice in defending the body.

However, this causes a problem. As Figure 1.I shows, the body reacts far faster when facing the same antigen for a second time, even faster for a third, still faster for the fourth, and so on. The problem occurs because the body has already primed itself against its self antigens, and in the absence of other antigens, has done this several times already.

Due to this priming, every time the body attacks its self antigens, it attacks them at a greater speed than ever. This reaches a point where it attacks itself so quickly, and attacks so many antigens within itself at the same time, that suppressor T-cells, however mature, are unable to stop it. An autoimmune disease is formed, and the immune system is out of control.

The Presence of More Professional APC’s/Immune Cells

Professional APC’s (Antigen Presenting Cells), are parts of the human body that confirm T-cells, and activate them. Since the immune system at a young age does not fight outside infection in those raised in a pathogen-free environment, this allows for the number of professional APC’s and the general number of immune cells to increase without check through infection.

Due to the increase in the number of professional Antigen Presenting Cells, as soon as the first infection takes place, the number of activated T-cells is far more than in a normal human body. As well, once cells such as cytotoxic T-cells have been activated once, they no longer need to be verified in the future and have matured. Furthermore, since only one infection has been fought off, the number of activated T-cells is large, and this causes an increase in the number of antigens they respond to, including self-antigens. This may cause an increase in autoimmune diseases and allergies, not all of which the body is able to suppress.

As well, the lack of early infections causes a general increase in the number of immune cells in the body. Again, this increased number of immune cells is able to respond to more antigens, especially those antigens that are ever-present in the body: self antigens that belong to the body. Hence, the presence of more professional APC’s to help T-cells mature and the presence of more immune cells in order to respond to more antigens is likely a cause of the lack of autoimmune diseases and allergies in those children brought up in sterile environments.

As Theorized by Others

Other scientists, such as Graham Rook, a professor at the Centre for Infectious Diseases and International Health at the Royal Free and University Medical School in London, UK, have also theorized about the cause of this higher rate of autoimmune diseases and allergies in those who grew up in clean environments. Rook thinks that there may be certain pathogens that are now missing from our environments that induced tolerance in our bodies because they were simply too big to fight, or were required by the body.

A case in point is the hemlinth. Once something that large managed to defeat the body’s physical barriers and to infect the body, the immune system would simply have to tolerate it, using immunoregulation. Since what Rook calls “old friends” are no longer present in our environments, the immune system is no longer able to prime itself in the absence of such pathogens, and is susceptible to attacking itself.

In Response to the Hypothesis

“If a child raised in a pathogen free environment has more allergies and is worse at dealing with autoimmune diseases, then the primary factor is experience at fighting diseases and ignoring more minor problems, because the immune system is so complex. It is likely that many parts of the immune system are activated as pathogens arrive in the system (such as suppressor T-cells), and these may not be able to function as well without regular “practice”, which is given by minor pathogens.”

The hypothesis was correct in stating that there are a number of factors involved in causing the increase in autoimmune diseases and in the immune system being worse equipped to deal with such diseases. It was also correct in stating that part of the reason was that the immune system may ignore more minor problems while fighting diseases, as well as that more suppressor T-cells will be activated as pathogens attack the body, because both of these facts have either been proven in studies, or are supported through further research. However, in stating that experience and practice had anything to do with the immune system, it was incorrect, because the immune system does not function in a manner where experience and practice have a significant role to play.

Reliability of Results

Since this project is a research project, it is impossible to investigate the reliability of the results obtained without actually testing the results in an experiment. If each postulation were to be individually tested, then the cause could be isolated as a definite answer to the problem.