Mean Platelet Volume is Increased Only by Subcutaneous Allergen Immunotherapy But not in Allergic Diseases

Amaç: Trombositler hemostaz yanında inflamasyonun patogenezinde rol oynar. Ortalama trombosit hacmi (MPV) trombosit aktivasyonunun biyolojik belirteci olarak kullanılır. Allerjik hastalıkların patogenezinde trombositlerin rolünün iyi bilinmesine rağmen MPV değeri allerjik hastalıklarda halen tartışmalıdır. Çalışmanın amacı Allerjik hastalıkları olan hastalarda ve subkutan venom ve aeroallerjen immünoterapisi alan hastalarda MPV değerindeki değişiklikleri izlemektir.


INTRODUCTION
Platelets play an important role in various physiological functions such as haemostasis, wound healing and inflammation (1,2).Platelet activation is associated with a rapid intracellular reorganization of actin and microtubule components of the cytoskeleton.This reorganization produces a considerable enhancement of the platelet surface area.More active platelets therefore tend to exhibit a larger volume than do less active platelets (3).MPV is the indicator of the average size of platelets and is increased after activation (4).MPV is now automatically estimated by the vast majority of commercial hematologic analyzers (5), thus providing an inexpensive, easy, fast and reliable parameter to help studying thrombocyte activation in many diseases.The relevance of MPV has been clearly underlined in studies carried out in patients with chronic inflammatory conditions (6)(7)(8)(9)(10)(11). Some of these studies have found that value of MPV is elevated (6,7,10).In contrast, others have reported that the value of MPV are reduced (8,9,11).
Platelets have been shown to express both highaffinity and low-affinity IgE receptors on their surfaces (12).Therefore, they are thought to play a role in allergic inflammation.Alterations of MPV value have been shown in allergic diseases like chronic urticaria and asthma (13,14).Although these studies have contradictory results, the changing of MPV values could indicate inflammation in general.The aim of this study was to investigate the values of MPV in children with atopic dermatitis, food allergy, chronic urticaria, allergic rhinitis and obese asthmatics.
Based on these studies, we hypothesized that MPV levels would change during AIT.AIT, which is the only way of changing the destination of allergy, changes the response to allergen exposure by inducing immunological tolerance.Allergen-specific T cells are activated, leading to an inflammatory reaction.Therefore, we evaluated whether there was any effect of AIT on the changes of MPV in children with asthma and venom anaphylaxis during IT.

MATERIALS and METHODS
This hospital-based, cross-sectional study was conducted in patients with atopic dermatitis, food allergy, chronic urticaria, allergic rhinitis, and asthma, and on obese asthmatics.The control group included age-and gender-matched healthy controls.We also evaluated the changes in the value of MPV by both venom and aeroallergen IT.The values were compared with those at the beginning and at the second year of SCIT.The study was approved by the local ethics committee.
The patients with atopic dermatitis were grouped as mild, moderate and severe using the "severity scoring of atopic dermatitis" index.All patients with food allergy had IgE-mediated food allergies.Patients with chronic urticaria were evaluated based on a positive and negative autologous serum skin test.All the patients with allergic rhinitis were sensitive only to grass pollens.Blood samples were taken from these patients in season and off season.All the patients with asthma and obese-asthma were under treatment and control.
A conventional protocol was used for VIT, pollen immunotherapy and house dust mite immunotherapy groups.After reaching the maintenance dose, injection intervals were every 4 weeks throughout the maintenance phase.Injections were administered subcutaneously at the distal lateral aspect of the upper arm.
Venous blood samples were collected in vacuette tubes.Complete blood count analyses were performed using a Coulter MaxM device (Beckman Coulter).

Statistical Analysis
Statistical analyses were performed using the SPSS software, version 20.The variables were investigated using visual (histograms, probability plots) and analytical methods (Kolmogorov-Smirnov/Shapiro-Wilk's test) to determine whether or not they were normally distributed.Descriptive analyses were presented using medians and interquartile range (IQR) for the non-normally distributed and ordinal variables.Since the age and MPV levels were not normally distributed; nonparametric tests were conducted to compare these parameters, as well as to compare the ordinal variables.The Mann-Whitney U test was used to compare MPV levels between the patient and the control groups.The Wilcoxon test was used to compare the change in MPV levels between baseline and second years in the SCIT group.A p-value of less than 0.05 was considered to show a statistically significant result.

DISCUSSION
The main finding of the study is that MPV value gradually increased in patients with receiving aeroallergen IT and VIT groups.Secondly, there was no difference observed in values of MPV in patients with allergic diseases.
Recently, MPV value has been studied in various allergic diseases as a marker of activation.The MPV value is accepted as one of the potential indicators of platelet production and consumption (15).It has been suggested that changes in the value of MPV are correlated with the function and activation of platelets (16,17).
There is no consistency between studies showing MPV changes in allergic diseases.Unlike other studies, MPV changes were assessed in patients with various allergic diseases in our study.There is only one study assessing the MPV change in atopic dermatitis in the literature.In this study, while the MPV level was higher in patients with atopic dermatitis compared to the control group, no correlation was found with the disease severity (18).In our study, we found that the disease and its severity did not change the MPV values.
There is no study evaluating the relationship between food allergy and MPV value so far.We have found that there is no difference between the patients with IgEmediated food allergy and the control group in terms of MPV values in our study.
The studies evaluating MPV changes in allergic diseases have mostly been in patients with chronic urticaria and controversial results have been obtained.Kasperska-Zajac et al. (19) reported no difference between the patients with chronic spontaneous urticaria and control group in terms of MPV values.Chandrashekar et al. have shown that MPV values are higher in the group with chronic spontaneous urticaria (20).Moreover, it has been shown that MPV values are higher in those having a positive autologous serum test compared to those having a negative autologous serum skin test (20).Magen et al. similarly, showed that MPV values in the patients with chronic spontaneous urticaria who have positive autologous serum skin test are higher than the patients with negative autologous serum skin test and the control group (14).In our study, however, there was no difference between the group with chronic spontaneous urticaria and the control group in terms of MPV values and similarly, MPV values were not different between those having a positive autologous serum skin test and those having a negative autologous serum skin test.
MPV value in patients with allergic rhinitis has not been evaluated so far.There was no significant change in terms of MPV value between the patients with allergic rhinitis and the control group.Seasonal differences did not affect the values of MPV in the patients with allergic rhinitis.
A relationship has been shown between obesity and MPV values (21).For the first time, MPV values were studied in the patients with coexistence of asthma and obesity and no difference was detected.
Although MPV values are controversial in allergic diseases, our study has shown that especially the MPV values change over time in patients receiving pollen IT, house dust mite IT and VIT.

Kowal et al. have shown the advent of platelet activation
developed by allergen challenge (22).They evaluated platelet counts, plasma levels of beta thromboglobulin, platelet factor-4 and soluble p-selectin in DP sensitive asthmatic patients prior to and after challenge with DP periodically at the 30 th minute, and 6 th and 24 th hours.In this study, eleven patients responded to allergen challenge only in the early phase, and 22 patients responded to the allergen challenge both in the early and late phases.In the early responsive group, platelet counts decreased for the first 30 th minute and markers of platelet activation in plasma increased.While markers of platelet activation were found to be high, platelet counts were lower both in the early and late phases in the dual responsive group.Prechallenge platelet activation status was not different than the control group (22).In a previous study it was shown that circulating platelet activity, the measure of beta-TG, in patients with grass-pollen induced intermittent rhinitis during the course of the dose increase phase of grass pollen SIT did not show any significant changes (23,24).Besides, a recent study showed that platelet activation is inhibited significantly during sublingual immunotherapy (25).In our study, changes of MPV values and platelet counts could be explained by allergen exposure as it is applied in allergen immunotherapy.Having MPV changes in VIT like allergic inflammation is another interesting result of our study.As mentioned in the studies where an allergen challenge has been applied and platelet activation evaluated, a response 24 hours later than the challenge is considered a late response.The evaluation of MPV in patients receiving immunotherapy has been done before the next dose of immunotherapy and an average of 20 days has passed after applying the last allergen immunotherapy.MPV, markers of activation of platelets, increased over time in patients receiving IT.According to this result, it can be concluded that platelets might have a function in immunomodulation mechanisms.
In conclusion, this study has underlined that MPV changed significantly over the years in SCIT.

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The severity of atopic dermatitis did not affect the values of MPV significantly.The values of MPV was not also significantly different in the patients with chronic urticaria whose autologous serum skin tests were positive or negative [8 (7.4-8.5)fl and 8 (7.5-8.6)fl respectively].An effect of seasonal differences was not observed in patients with allergic rhinitis and asthma.No difference was detected in MPV levels in season and off season [in season MPV median (IQR) 8.5 (7.7-9.1)fl, off season MPV 8.6 (7.9-9.2) fl].

Figure 2 .
Figure 2. The changes of MPV values during immunotherapy.A) Aeroallergen immunotherapy group.B) Venom immunotherapy group.MPV0: MPV level before IT, MPV1: MPV level after 1 year of IT, MPV2: MPV level after 2 years of IT.