Adenoid hypertrophy is the most common cause of upper airway obstruction in pediatric populations, and is associated with heightened immunologic activity [1,2]. It frequently results in obstructive sleep apnea (OSA), leading to a spectrum of morbidities, including mouth breathing, intermittent hypoxia, sleep fragmentation, asthma, nasal obstruction, and speech impairment. Severe cases may lead to craniofacial abnormalities and cognitive deficits [[3], [4], [5], [6], [7]]. Epidemiological data indicate that AH affects up to 49.70 % of pediatric populations [8]. Despite its high prevalence and clinical significance, the pathogenesis of AH remains poorly understood, with limited molecular insights compared to other common pediatric conditions [9]. Adenoidectomy is widely recognized as the most effective treatment for AH, but it is associated with complications such as postoperative pain and hemorrhage, imposing a considerable burden on both patients and healthcare systems [10]. Thus, a comprehensive investigation into the pathophysiological changes, underlying molecular mechanisms, and potential therapeutic targets for AH is urgently needed.

The adenoid is a mucosa-associated lymphoid organ situated on the posterior wall of the nasopharyngeal apex, functioning as a critical component of the mucosal immune barrier in both the respiratory and digestive tracts [11]. Enriched with lymphoid follicles and diverse immune cell populations, it forms an integral part of Waldeyer's ring [12]. Previous studies have implicated pathogenic infections in the development of AH, which is associated with quantitative and functional alterations in lymphocyte subsets within the adenoid tissue [13]. The shift in lymphocyte composition has traditionally been considered a key pathological mechanism underlying the condition [14,15]. However, these observations were predominantly derived from histological or biochemical analysis, which only captured limited pathological features. Recent investigations employing genomic profiling in AH samples have revealed dysregulation of local immune responses; however, precise, cell type-specific molecular signatures remain unclear due to the inherent limitations of bulk-input approaches [16]. Furthermore, although earlier studies have reported shifts in the proportions of classical lymphocyte subsets and cytokine profiles, specifically, an increase in naïve lymphocytes and a decrease in effector lymphocytes in AH [17], the involvement of key transcription factors (TFs) in lymphocyte subset regulation, as well as the nature of intercellular communications among these subpopulations, remain poorly understood.

The adenoid is primarily composed of lymphoid tissue. Although its cellular composition is relatively simple, dysfunction in any cell type can potentially result in serious consequences [18]. However, the cellular heterogeneity within adenoid tissue remains largely unexplored. Single-cell RNA sequencing (scRNA-Seq) provides unprecedented high-resolution for investigating disease mechanisms. While scRNA-Seq has been applied to various lymphatic tissues, most studies have focused on lymphoma [[19], [20], [21], [22]]. A comprehensive single-cell characterization of the cellular landscape, immunological microenvironment, and molecular etiology of AH is lacking.

In this study, we performed scRNA-Seq analysis of adenoid tissues from pediatric patients with mild to moderate hypertrophic adenoids (MHA) and severe hypertrophic adenoids (SHA) to elucidate cell-type-specific transcriptional alterations in AH. Through comprehensive bioinformatic analyses, we delineated the cellular composition, differential gene expression patterns, and intercellular communication networks within the adenoid microenvironment. We focused particularly on B cell subsets and their developmental regulators [[23], [24], [25]], as well as interactions among immune cell subsets implicated in AH pathogenesis. This work provides valuable insights into the molecular mechanisms underlying AH and establishes a foundation for the development of targeted therapeutic strategies for this prevalent pediatric condition.