Analysis of T cell responses to the major allergens from German cockroach: epitope specificity and relationship to IgE production

Abstract

Bla g allergens are major targets of IgE responses associated with cockroach allergies. However, little is known about corresponding T cell responses, despite their potential involvement in immunopathology and the clinical efficacy of specific immunotherapy. Bioinformatic predictions of the capacity of Bla g 1, 2, 4, 5, 6, and 7 peptides to bind HLA-DR, -DP, and -DQ molecules, and PBMC responses from 30 allergic donors, identified 25 T cell epitopes. Five immunodominant epitopes accounted for more than half of the response. Bla g 5, the most dominant allergen, accounted for 65% of the response, and Bla g 6 accounted for 20%. Bla g 5 induced both IL-5 and IFN-γ responses, whereas Bla g 6 induced mostly IL-5, and, conversely, Bla g 2 induced only IFN-γ. Thus, responses to allergens within a source are independently regulated, suggesting a critical role for the allergen itself, and not extraneous stimulation from other allergens or copresented immunomodulators. In comparing Ab with T cell responses for several donor/allergen combinations, we detected IgE titers in the absence of detectable T cell responses, suggesting that unlinked T cell-B cell help might support development of IgE responses. Finally, specific immunotherapy resulted in IL-5 down modulation, which was not associated with development of IFN-γ or IL-10 responses to any of the Bla g-derived peptides. In summary, the characteristics of T cell responses to Bla g allergens appear uncorrelated with IgE responses. Monitoring these responses may therefore yield important information relevant to understanding cockroach allergies and their treatment.

Figure 1. Peptide binding predictions allowed efficient identification of a preponderance of the Bla g specific T cell response

Bla g allergen sequences were scanned with a panel of bioinformatics algorithms predicting binding to 20 common HLA class II molecules, as described in the materials and methods. Peptides were ranked on the basis of predicted binding promiscuity, and all peptides predicted to bind 7 or more molecules were selected for synthesis and tested for recognition in allergic donors. Then cumulative Bla g specific response (total SFC) as function of peptide rank was tabulated. Saturation of responses was noted at a rank of about 160, corresponding to approximately the top 35% scoring peptides, and over 75% of the response was associated with the top 100 (corresponding to the top 22%) predicted peptides.

Figure 2. Inferred HLA restriction of T cell responses to Bla g epitopes

The HLA restriction of donor responses to Bla g epitopes was determined in selective cases using cell lines transfected with a single HLA class II molecule and/or the use of HLA matched (+)/mismatched (−) EBV transformed cell lines. Representative data are shown.

Figure 3. Polarized T cell responses to Bla g antigens within an individual donor

T cell responses against Bla g allergens are differentially polarized at the level of individual donors. IFNγ (black bars) and IL-5 (gray bars) responses in donor U00023 to epitopes derived from Bla g 2 (epitope region 5, Bla g 2.11–25, and epitope region 7, Bla g 2.46–60) and Bla g 6 (epitope region 23, Bla g 6.6–20) are shown. The T cell response to Bla g 6 was associated only with only IL-5 production, while the response to the two Bla g 2 epitopes was only associated with IFN-γ.