Association of allergen-specific regulatory T cells with the onset of clinical tolerance to milk protein

Background

About 70% of children with milk allergy tolerate extensively heated milk (HM) products and outgrow their allergy earlier than those who react to HM.

Objective

To test the hypothesis that HM-tolerant children have a higher precursor frequency of adaptive allergen-specific regulatory T (Treg) cells.

Methods

Allergic, HM-tolerant, outgrown, or control subjects were defined by oral food challenge. PBMCs were cultured with purified caseins and controls for 7 days, and proliferating CD25⁺CD27⁺ Treg cells were identified by flow cytometry. Proliferating cells were also characterized for their expression of FoxP3, CTLA 4, CD45RO, and CD127. Allergen-specific Treg cell origin and function were assessed by depletion of CD25^hi cells before culture.

Results

There was a higher percentage (median [25th% to 75th%], 16.85% [7.1-31.7]) of proliferating allergen-specific CD25⁺CD27⁺ T cells from cultures of HM-tolerant subjects (n = 18) than subjects with allergy (n = 8; 4.91% [2.6-7.5]; P < .01). Control subjects with no history of milk allergy (n = 7) also had low percentages of these cells (2.9% [2.4-6.0]), whereas outgrown subjects (n = 7) had intermediate percentages (9.0% [2.7-16.4]). There were no significant differences between the patient groups in the frequency of polyclonal Treg cells or allergen-specific effector T cells. Allergen-specific Treg cells were found to be FoxP3⁺CD25^hiCD27⁺, cytotoxic T lymphocyte–associated antigen 4⁺, CD45RO⁺CD127⁻ and were derived from circulating CD25^hi T cells. Depletion of the CD25^hi cells before in vitro culture significantly enhanced allergen-specific effector T-cell expansion.

Conclusion

A higher frequency of milk allergen-specific Treg cells correlates with a phenotype of mild clinical disease and favorable prognosis.

Key words: Treg, FoxP3, CTLA-4, immune tolerance, oral tolerance, food allergy, milk allergy

Abbreviations used: CTLA, Cytotoxic T lymphocyte–associated antigen, HM, Heated milk, NHM, Nonheated milk, Treg, Regulatory T