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.