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Keywords:

  • allergic rhinitis;
  • bronchial asthma;
  • hypersensitivity;
  • polysensitization;
  • skin prick test

It has been shown that the concomitant presence of multiple sensitizations and the number of sensitizing allergens positively correlate at a certain extent with the severity of symptoms of rhinitis and asthma. In detail, clinical studies suggested that patients sensitized to, and simultaneously exposed to, multiple allergens exhibit more symptoms than monosensitized individuals (1–3). Recently, Nopp et al. (4) demonstrated that IgE antibodies with different specificities can have an additive effect on the activation and consequent release of mediators from basophils of polysensitized subjects. On the basis of this background, we evaluated, via the skin prick test (SPT) model, if the association of two noncrossreacting allergens can increase the magnitude of the skin response, in comparison with single allergens.

Sixty patients aged between 14 and 59 years (mean age 30.5; 27 male patients), suffering from rhinitis and/or asthma, and sensitized to at least six inhalant allergens, as assessed by SPT, were studied. Thirty healthy and SPT-negative subjects, aged between 14 and 74 years (mean age 38.5; 12 male patients), served as controls. Two mixtures of allergens, indoor and outdoor were prepared for the test. One contained Dermatophagoides pteronyssinus (D) 50% + Cat dander (C) 50% and one contained Parietaria (P)50% + Timothy grass pollen (G) 50%. Both mixtures, D + C and P + G, as well as the single allergens were diluted with a glycerinated solution at 1 : 8; 1 : 32 and 1 : 64 to identify a dose–response effect. Allergenic materials and diluents were kindly supplied by Lofarma Laboratories (Milan, Italy). Duplicate SPTs were carried out on both forearms and read according to international guidelines (5). The results were expressed as the mean of the major diameter of the wheal plus its orthogonal, and analyzed by one-way variance analysis and Bonferroni’s t-test.

There was a significant difference in the wheals’ diameters between the mixtures and the single allergens, for both the indoor and outdoor allergens and for all concentrations as shown in Fig. 1. The mean wheal diameters for indoor allergens were: D + C (6.61 ± 1.19mm), D (5.40 ± 0.72mm) and C (3.59 ± 0.83mm) with a P-value of <0.001 for the mixture vs the single allergens. Similarly, for pollen allergens, the diameters were: P + G (6.91 ± 0.98mm), P (5.60 ± 0.65mm) and G (5.07 ± 0.79mm) again with a P-value of <0.001. The only exceptions were D + C vs D and P + G vs P at 1 : 32 and 1 : 64 dilutions. No SPT response was seen in control individuals.

image

Figure 1.  Mean diameter of the wheal obtained at the skin prick test (SPT) with the different concentrations. Significant differences between mixtures and single allergens are indicated above the bars.

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The larger mean diameters of wheals induced by using a mix of two allergens, in comparison with the single one, suggest an additive effect of multiple proteins on histamine release from cutaneous mast cells. Our findings obtained from an in vivo model confirm the additive effect of multiple allergens on basophils demonstrated in vitro by Nopp et al. (4). Moreover, these data may suggest a change in our interpretation of the potential role of the single allergen in the context of a polysensitization. Each single allergen could be of limited clinical significance, but a simultaneous exposure to several allergens may induce a greater release of the mediators and, consequently, a higher degree of respiratory symptoms. Because of the increasing number of polysensitized patients, this interpretation could determine potential implications and deeper understandings in the therapeutic management of allergic patients, for instance with immunotherapy and anti-IgE antibodies.

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