Allergies: Helminth Theory

As a species, humans have recently become vunerable to allergies.  Even if your parents are asked, they will say allergies were not as much of a concern as they were not.  One theory explaining the prevelence of allergies in humans, particularly those of first world countries involves helminth infections.  When an antigen enters the human body, the antigen bind to T cells which then stimulate B cells.  B cells differentiate to form antibodies like IGF which binds to other cells of the immune system and arm them against the antigen.  IGF is an important form of antibody because it is key to the fighting of helminth infections.  The armed cell can then react to antigens like cats and dust that do not pose of risk to the health of the individual.  In populations with high levels of helminth infections, the IGE levels are very high compared to populations lacking helminth infections and none of the individuals have allergies.  It is thought that the helminth infections keep the IGE "busy" so it does not have time to react to antigens that are not dangerous (those causign allergic reactions).