Cross-reactions
Cross-reactions play an important role in the PHM hypothesis. Trost et al[21] found that “no human protein is exempt from bacterial motifs.” This extensive cross-reactivity may be quite significant. It might be that plant microbiomes have a similar level of cross-reactivity with plant proteins. This might mean that food hypersensitivity of multiple types might be at least partly due to microbial antigens found in plants cross-reacting with food allergens. Plant microbes that increase after harvest and thus reach elevated levels in stored food (both from plants and potentially the animals that consume them) might be a source of cross-reacting PHM. These cross-reactions could magnify the effect of low-level microbial colonization.
The level of colonization by a PHM could explain why one person reacts to a particular substance and another does not. The location that the microbe has colonized could potentially determine the type and location of the reaction. For instance, colonization of the skin might lead to atopic dermatitis, colonization of the intestines might lead to diarrhea, and colonization of blood vessels might lead to cardiovascular signs and symptoms.
Cross-reactions might be a significant part of the processes that lead to chronic inflammatory disease, as suggested by two recent examples. Bacher et al[22] provided evidence that a cross-reaction between intestinal C. albicans and lung Aspergillus fumigatus could, under certain circumstances, lead to the inflammatory lung disease, allergic bronchopulmonary aspergillosis. These two fungal species could be considered to be PHM. High A. fumigatus exposures can occur with certain farming exposures or due to water-damaged buildings. C. albicans overgrowth might arise from a westernized diet and antibiotics, as mentioned above.
The second example is a recent study[23] that found that Pseudomonas fluorescens, an environmental bacteria, cross-reacts with gliadin and might possibly be linked to celiac disease. P. fluorescens is cold-tolerant and can survive in refrigerated food, and is found in moldy buildings and on walls and shower fixtures[24]. Thus, it is potentially a PHM.