Response of respiratory flour allergics in an ingested flour challenge may involve plasmacytoid dendritic cells, CD25+ and CD152+ T cells.

Background: A number of occupational respiratory allergens are food related, and little is known about the responses these allergens elicit in sensitized persons that ingest them.

Methods: Nine respiratory flour-allergic volunteers were exposed in a double-blind placebo-controlled food challenge with flour. Responses were monitored by spirometry, acoustic rhinometry, determination of urinary methyl histamine and tryptase and flow cytometric evaluation of basophil, dendritic and T cell numbers and markers.

Results: Significant increases in serum tryptase (compared with placebo post-exposure levels) and methyl histamine and a coordinated decrease in blood basophils and nasal volume after ingestion of allergen compared with placebo suggest an allergic response to ingested allergen. There was no change in forced expiratory volume in 1 s. The number of blood plasmacytoid dendritic cells (DC), but not of myeloid DC, decreased after exposure (p = 0.001). DC HLA DR was reduced after both exposures (p < 0.001). Expression of CXCR4 on DC was reduced after allergen (p = 0.033) but not after placebo exposure. CD4+ T cell expression of CD25 was elevated after placebo (p = 0.021) but reduced after allergen provocation. The reduction in CD25 expression after allergen compared with placebo was significant (p = 0.024). CD152 was downregulated on these cells after allergen (p = 0.039) but less so after placebo exposure.

Conclusion: Persons with respiratory allergy respond after ingestion of the relevant allergen. Response to this allergen challenge may selectively recruit plasmacytoid DC through CXCR4 and T cells expressing CD25 and CD152, which may be a regulatory phenotype.