Decreased numbers of metachromatic cells in nasal swabs in Japanese cedar pollinosis following sublingual immunotherapy

The Improvement in Symptoms After Sublingual Immunotherapy for Japanese Cedar Pollinosis Coincided With the Reduction in Nasal Metachromatic and Eosinophilic Cells

Background and objectivePreviously, it was reported that droplet SLIT in Japanese cedar pollinosis reduced metachromatic cell and eosinophil counts in nasal swabs along with symptom improvement. In this study, it was confirmed that SLIT using tablets also reduces the number of these cells along with symptom improvement, and examined the time course of these effects.MethodsOne hundred twenty-one visits of 57 subjects treated with SLIT occurred in our clinic between January 16 and April 8, 2023 (Jc pollen season). The 57 patients had been receiving SLIT for 0.16 to 7.8 yr, and symptoms were assessed using a self-reported questionnaire. Nasal swab cytology was used to compare the reduction in Mc, eosinophil and neutrophil numbers with that of non-SLIT 110 subjects. We then investigated the timelines of the decrease in Mc and eosinophils and their relationship to symptoms.ResultsC Subjects who received SLIT had significantly reduced moderate to most severe symptoms compared to non-SLIT subjects over the Jc pollen season. There was symptom improvement for subjects with ≤2 yr SLIT treatment, but more improvement after >2 yr of SLIT treatment. Mc and eosinophil numbers in nasal swabs of SLIT subjects were significantly lower than in non-SLIT subjects. Moreover, levels of eosinophilia decreased within 2 yr of SLIT treatment, but further decreased with >2 yr of SLIT. Mc numbers in subjects with >2 years of SLIT were significantly lower than in non-SLIT subjects. There was no significant difference in neutrophil numbers in nasal swabs between non-SLIT and SLIT subjects.ConclusionSLIT administered by tablet was effective in improving symptoms within 2 yr, and further improved after 2 yr. The eosinophil counts also decreased within 2 yr, and further decreased over 2 yr. The Mc count significantly decreased only after 2 yr of SLIT treatment.

Sublingual Immunotherapy: How Sublingual Allergen Administration Heals Allergic Diseases; Current Perspective about the Mode of Action

Owing to the successful application of sublingual immunotherapy (SLIT), allergen immunotherapy (AIT) has become one of the leading treatments for allergic diseases. Similar to the case with other AITs, such as subcutaneous and oral immunotherapies, not only the alleviation of allergic symptoms, but also the curing of the diseases can be expected in patients undergoing SLIT. However, how and why such strong efficacy is obtained by SLIT, in which allergens are simply administered under the tongue, is not clearly known. Various potential mechanisms, including the induction of blocking antibodies, T cell tolerance, regulatory B and T cells, CD103^-CD11b⁺ classical dendritic cells, and CD206⁺ macrophages, and the reduction of innate lymphoid cells, mast cells, and basophils, have been suggested. Recently, through a comparative analysis between high- and non-responder patients of SLIT, we have successfully proposed several novel mechanisms. Here, we introduce our recent findings and summarize the current understanding of the mechanisms underlying the strong efficacy of SLIT.

Decreased numbers of metachromatic cells in nasal swabs in Japanese cedar pollinosis following sublingual immunotherapy

Background and Objective

Nasal symptoms were reduced following allergen‐specific sublingual immunotherapy (SLIT) for allergic rhinitis. The mechanisms underlying the effectiveness of SLIT for Japanese cedar pollinosis are poorly understood. We studied changes in the numbers of metachromatic cells, eosinophils, and neutrophils following SLIT for Japanese cedar pollinosis.

Methods

Nasal swabs were taken in the preseason (n = 32) and in pollinosis season (n = 49) from subjects given sublingual drop immunotherapy for an average duration of 1.5 years. The numbers of metachromatic cells (mast cells and basophils), eosinophils and neutrophils were determined and compared with those from untreated subjects in preseason (n = 65) and in season (n = 54).

Results

SLIT subjects had a significantly reduced frequency of moderate to most severe symptoms in comparison to untreated subjects in preseason (P < .001, the Mann‐Whitney U test), and (P < .00001) in season. Metachromatic cell counts in nasal swabs of SLIT subjects in preseason and in season were lower than those of untreated subjects (P = .014, the Mann‐Whitney U test) and (P = .00001) respectively. Eosinophil numbers in SLIT subjects were not significantly different than in untreated subjects in both preseason (P = .29) and in season (P = .09). However, when SLIT subjects in season were divided into those with greater than or equal to 1.5 years, or <1.5 years of SLIT duration, the degree of eosinophilia in those with SLIT greater than or equal to 1.5 years was significantly lower (P = .011) than in untreated patients, but not in those with SLIT less than 1.5 years (P = .9). There were no significant differences in neutrophil numbers in nasal swabs between untreated and SLIT subjects in preseason and in season.

Conclusion

One of mechanisms underlying the effectiveness of sublingual drop immunotherapy for Japanese cedar pollinosis is a reduction of the number of metachromatic cells in preseason and in season. Eosinophilia was also reduced in season in those given SLIT for greater than or equal to 1.5 years.