Cross-reactions
Cross-reactions play an important role in the PHM hypothesis. Trost et
al[100] found that “no human protein is exempt from bacterial
motifs.” The extensive cross-reactivity they found between only 40
bacterial species and human self-tissue is significant. It also may have
implications for agricultural products. It seems plausible that the
plant-associated microbiota would have a similar high level of
cross-reactivity with plant proteins. The PHM hypothesis proposes that
food hypersensitivity might be at least partly related to
plant-associated microbial antigens cross-reacting with known food
allergens.
Plant microbes that increase after harvest and reach elevated levels in
stored food might be a source of PHMs that colonize humans. PHMs would
also likely be present in animal products, due to the animals’
microbiotas including PHMs they acquired from their food and other
sources. Cooking eliminates most of the microbes but is likely
insufficient to eliminate all PHMs.
Cross-reactions are a potentially significant factor in CIDs as
suggested by two recent examples. Bacher et al[101] provided
evidence that a cross-reaction between two fungi, intestinal C. albicans
and lung A. fumigatus, could lead to the inflammatory lung disease,
allergic bronchopulmonary aspergillosis. Both fungi might be considered
to be PHMs. High A. fumigatus exposures can occur in farming[102] or
in damp or water-damaged buildings[103,104]. C. albicans overgrowth
might be related to westernization-associated factors, such as
diet[105] and medication[106].
Another example is a study[107] that found that Pseudomonas
fluorescens cross-reacts with gliadin and might be linked to celiac
disease. P. fluorescens can survive in refrigerated food and is found in
moldy buildings, on walls and shower fixtures[108] and thus might be
a PHM.