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.