Natural and Induced Tolerance to Hymenoptera Venom: A Single Mechanism?

Abstract

Inducing tolerance in Hymenoptera-allergic patients, bee venom immunotherapy (BVIT) is a widely accepted method to treat severe allergy to bee stings. In order to increase the existing knowledge on the underlying immunological mechanisms and look for possible biomarkers predictive of efficacy, a group of 20 bee-venom-allergic patients (AG) were thoroughly examined during their first year of BVIT. In addition, the results of treated patients with those of an untreated group of 20 tolerant beekeepers (TG) who had previously shown a firm suppressor-regulatory profile were compared. Tolerance in AG patients was invariably associated with a significant regulatory response characterised by the expansion of Helios^- subpopulation and increased IL-10, specific IgG4 (sIgG4), and kynurenine levels. Although specific IgE (sIgE) levels increased transiently, surprisingly, the T helper type 2 (Th2) population and IL-4 levels rose significantly after one year of immunotherapy. Thus, the picture of two parallel phenomena emerges: a tolerogenic response and an allergenic one. Comparing these results with those obtained from the TG, different immunological mechanisms appear to govern natural and acquired tolerance to immunotherapy. Of particular interest, the kynurenine levels and T regulatory (Treg) Helios^- population could be proposed as new biomarkers of response to BVIT.

Keywords: Helios protein; anaphylaxis; bee venom immunotherapy; kynurenine; tolerance.

Figure 1

Percentage of CD4⁺Th1 (A) and Th2 (B) subsets of the allergic group (AG, pink) throughout the BVIT course and tolerant group (TG, green) when priming the culture with 1 µg/mL of AmV. The mean and standard error of the mean bars is displayed. At the top of the plot, mixed-effect model p-values of time are shown, establishing T0 as the baseline level, whereas at the bottom, unpaired t-tests (for equal or unequal variances) or Mann–Whitney U tests to compare the mean in each time respect to TG are considered.

Figure 2

Percentage of peripheral blood CD4⁺CD25^highCD127^low (A), Helios⁻ (B), and CTLA-4⁺ (C) Treg cells of the allergic group (AG, pink) throughout the BVIT course and tolerant group (TG, green). The mean and standard error of the mean bars are displayed. At the top of the plot, mixed-effect model p-values of time are shown, establishing T0 as the baseline level, whereas at the bottom, unpaired t-tests (for equal or unequal variances) or Mann–Whitney U tests to compare the mean in each time respect to TG are considered.

Figure 3

Percentage of activated basophils (%CD63⁺) of the allergic group (AG, pink) throughout the BVIT course and tolerant group (TG, green) when using 0.1 µg/mL (A) and 1 µg/mL (B) of AMv as a stimulus. The mean and standard error of the mean bars is displayed. At the top of the plot, mixed-effect model p-values of time are shown, establishing T0 as the baseline level, whereas at the bottom, unpaired t-tests (for equal or unequal variances) or Mann–Whitney U tests to compare the mean in each time respect to TG are considered.

Figure 4

Box-plots for the IL-10 (A) and IL-4 (B) levels (pg/mL) quantified in culture supernatant when priming the culture with 1 µg/mL of AmV and plasma kynurenine level (Kyn; ng/mL) (C) of the allergic group (AG, pink) throughout the BVIT course and tolerant group (TG, green). At the top of the plot, mixed-effect model p-values of time are shown, establishing T0 as the baseline level, whereas at the bottom, unpaired t-tests (for equal or unequal variances) or Mann–Whitney U tests to compare the mean in each time respect to TG are considered.

Figure 5

Box-plots for the sIgE level (left y-axis) and sIgG4 level (right y-axis) to AmV of the allergic group (AG, pink) throughout the BVIT course and tolerant group (TG, green). At the top of the plot, mixed-effect model p-values of time are shown, establishing T0 as the baseline level, whereas at the bottom, unpaired t-tests (for equal or unequal variances) or Mann–Whitney U tests to compare the mean in each time respect to TG are considered.

Figure 6

Box-plots for the serum-specific IgE level (sIgE; left y-axis) and specific IgG4 level (sIgG4; right y-axis) to Apis mellifera venom components (rApi m 1, rApi m 2, rApi m 3, Api m 4, rApi m 5, and rApi m 10; (A–F) panels) of the allergic group (AG, pink) throughout the BVIT course and tolerant group (TG, green). At the top of the plot, mixed-effect model p-values of time are shown, establishing T0 as the baseline level, whereas at the bottom, unpaired t-tests (for equal or unequal variances) or Mann–Whitney U tests to compare the mean in each time with respect to TG are considered. Table S1 shows the results in detail.

Figure 7

Timeline of the study for the treated allergy group.