Immunosuppression and disease persistence
The ability of many of these inflammatory diseases to benefit from
immunosuppressive therapies, such as corticosteroids, might be
considered contradictory to the PHM hypothesis. However, the apparent
benefit of immunosuppressive therapies in some chronic inflammatory
diseases may result from the suppression of an essentially ineffective
immune response against relatively low virulence microbes. High
virulence for their animal hosts is considered to be of questionable
value to many microbes[27], and thus low virulence may be quite
common.
According to the PHM hypothesis, the ineffectiveness of the immune
response against the PHM in chronic inflammatory disease is shown by the
persistence of the disease. This ineffectiveness could be due to varied
factors, including the microbes’ antigenic changes, heterologous
infection effects related to immunodominance, microbe-induced
Th1/Th2/Th17 imbalances, and microbes that produce substances that have
toxic effects on the immune system[1]. Chronic exposure or repeated
reinfection could also play a role.