Focal infection theory and bacterial allergy

As mentioned previously, the PHM hypothesis has some similarity to the early version of the focal infection theory, which also included the concept of bacterial allergy[2]. Desensitization to bacterial allergens was tested in several clinical trials and appeared to be successful in treating several CIDs, including chronic colitis[178], allergic rhinitis[179] and asthma[180,181]. Research found that autologous bacteria induced chemotaxis of peripheral blood mononuclear cells in non-atopic asthmatics but not controls[182], suggesting a role for hypersensitivity to colonizing bacteria. A review[181] concluded that bacterial vaccines (immunotherapy) were useful in at least a proportion of asthma cases.
However, a later review concluded that the evidence did not sufficiently support immunotherapy for bacterial allergens in asthma[183]. The discrepancy might be explained by an increasing effect of diverse, low abundance microbes, leading to decreasing effectiveness of approaches that focus on only a few bacterial species.
The PHM hypothesis suggests that earlier researchers using bacterial vaccines may have been increasing the ability of the immune system to reduce bacterial colonization, thus reducing symptoms. Similarly, one might speculate that some forms of current allergen-specific immunotherapy may be stimulating the immune system to eliminate at least some PHMs that cross-react with the known inhalant or food allergens. The elimination of the colonizing microbes by the immune system might be what leads to desensitization and reduction or elimination of symptoms in a proportion of patients.
The variation in severity of allergic reactions might reflect the levels of colonizing PHMs. Asymptomatic sensitization to allergens might be due to PHM colonization levels that are below the threshold needed for a detectable reaction.