Basophil activation test in oral desensitization to cow’s milk allergy

Abstract

The recent paper by Nucera et al., showed that the basophil activation test (BAT) in flow cytometry is able to monitor an acquired tolerance induced by a desensitization treatment in food allergy. The paper by Nucera et al. reported two standpoints in the CD63 response to food allergy and OAT and their large difference in CD63 response before and after suggests for the optimal performance of a CD123/HLADR/CD63 BAT in oral food allergy immunotherapy.

Dear Sir,

The recent paper by Nucera et al., ¹ in the latest issue of this journal, showed that the basophil activation test (BAT) in flow cytometry is able to monitor an acquired tolerance induced by a desensitization treatment in food allergy. BAT is a cellular test able to shed a light on the basophil response to molecules able to elicit an allergy-related mechanism, even in allergen immunotherapy. ² In the paper by Nucera et al., ¹ the authors aimed to show whether the analysis of cell activation markers usually used in BAT, such as CD63, would result in a reliable approach for monitoring the acquisition of clinical tolerance by specific oral desensitization in food allergy, such as egg or cow’s milk. Yet, Nucera et al. did not show any BAT result, as related to any of the three patients enrolled in the study. Although they employed a well suited test,^3,4 they were limited to presenting an exemplificative figure showing a BAT with CCR3 (CD193) gating strategy, despite the CD123-PE/HLA-DR-PerCP protocol indicated in Methods. They certainly stated about the finding of a significant reduction in CD63 expression level at the end of the cow’s milk desensitization protocol, but to what extent? Aside from data expressed in Table 2, without any statistical variance report, it would be very interesting to know the extent of this reduction and if the same is related to the CD63% parameter and its cutoff value, for which critical issues were recently reported. ⁵ In this circumstance, though restricted to a very narrow range of cases, BAT might give important insights about the “effectiveness” of an oral allergen therapy (OAT), particularly if BAT is able to follow up therapy as related to the allergen dosage and exposure times.^1,6 The authors showed a great difference in CD63 expression before and after OAT, using defined allergens such as α-lactoalbumin, β-lactoglobulin, and casein. In this circumstance, a more detailed dose–response and time–response evaluation of OAT in children should elucidate how the reported CD63 decrease in basophil membrane expression was due to OAT rather than other mechanisms involved in the spontaneous and physiological membrane recycling of CD63, particularly for allergens such as casein.^7,8 The rate of CD63 membrane upregulation, which should affect the CD63% evaluation at a BAT, depends strictly on cell endowment of CD63-intracellular pool and the ability to respond to defined allergens and different type of allergens; ⁸ therefore, during the OAT follow up, the CD63% effect of immunotherapy should be described in a dose- and time-dependent fashion. Furthermore, basophils are at a late time involved in the mechanism and particularly through the Th2-cell mediated immune response. A first response should be retrieved at the mucosal-IgA immunity. CD63 most probably is not easily activated by immune reactions in an IgE-mediated mechanism in mucosal tissues, ⁹ contrary to past reports showing an IgA-mediated basophil activation.^10,11 Yet, a close association between secretory-IgAs and pediatric food allergy was recently reported, ¹² and that serum IgE, as well as IgG1 or IgG4, might not correlate with food allergy, as well as IgA, depending on the type of food allergen. ¹³ This would mean that the reactivity of basophils to food allergens, measured by CD63 membrane expression, needs to be further evaluated on the basis of the different allergen, allergy individual systemic and mucosal response and OAT protocol, a perspective which compels the investigator to highlight OAT successful outcome by tracing CD63 expression throughout the whole OAT treatment and later follow up, as the membrane recycling and updisplacement of CD63 depends on this panoply of immune and humoral mechanisms.

The paper by Nucera et al. reported two standpoints in the CD63 response to food allergy and OAT and their large difference in CD63 response before and after suggests for the optimal performance of a CD123/HLADR/CD63 BAT in oral food allergy immunotherapy.