Mas‐Related G‐Protein Coupled Receptor‐X2 and Chemokine (C–C Motif) Ligand 2 Correlate With Disease Activity Among Treatment‐Naïve Chinese Patients With Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) often remains under-treated and significantly impacts quality of life [1-3]. The mainstay of treatment involves use of various mast cell-targeting medications, aiming for complete disease control [1, 4]. Although the use of patient-reported outcomes such as the weekly Urticaria Activity Score (UAS7) have been advocated, more objective biomarkers are needed [1, 4, 5]. Recent evidence have implicated the role of Mas-related G-protein coupled receptor-X2 (MRGPRX2) in CSU pathogenesis, with levels reported to correlate with disease severity [6, 7]. Blood tests such as MRGPRX2 are attractive biomarkers, given their ease of measurement and availability of commercial assays. However, to the best of our knowledge, studies correlating MRGPRX2 with CSU has not been validated beyond Korean patients [6]. Therefore, we conducted this study on a Chinese cohort to investigate the extended validity of serum MRGPRX2 as a biomarker, as well as its relationship with chemokine (C–C motif) ligand 2 (CCL-2), another potential biomarker reported to play a major role in CSU pathogenesis [8]. We enrolled newly diagnosed CSU patients referred to the Urticaria Clinic of the Hospital Authority Hong Kong West Cluster between 1 January 2023 and 31 July 2023. All patients were diagnosed according to the regional and international recommendations [1, 4]. Patient demographics, baseline characteristics, medication history and UAS7 were collected by standardised questionnaires with simultaneous bloods taken at first visit. To align with previous studies, UAS7 ≥28 and <28 patients were classified as 'severe' and 'nonsevere', respectively [1]. Treatment-naïve was defined by patients not taking any regular CSU medications for at least 1 month prior to enrolment. Serum MRGPRX2 levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit (MyBioSource, Inc., San Diego, CA, USA), and CCL2 levels were measured using Human CCL-2/MCP-1 instant ELISA kit (Thermo Fisher Scientific, MA, USA). No reference range was available for MRGPRX2, whereas CCL-2 levels ≥250 pg/mL were considered elevated based on previous studies. Statistical analyses were performed using IBM SPSS v22 (SPSS Inc., Chicago, IL, USA). Mann–Whitney U tests were used to determine the relation between baseline MRGPRX2 levels of severe and nonsevere patients; chi-squared tests were used to determine the relationship between CSU disease activity and CCL-2 levels; Pearson correlations were used to determine correlation between MRGPRX2 with UAS7 and CCL-2. Cut-off for significance levels for all tests were p < 0.05. Written informed consent was obtained from all study subjects. The study was approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster. A total of 95 patients were recruited, of which 47 (49%) were treatment-naïve. 75 (79%) and 20 (21%) of patients had severe and nonsevere disease at recruitment, respectively. Median age was 53 (19–20) years and the male: female ratio was 1:6.3. Overall, patients with severe disease had higher serum MRGPRX2 levels (severe: 41.06 ± 26.98; nonsevere: 26.64 ± 15.91 p = 0.011). Similarly, more patients with severe disease had elevated CCL-2 levels (70.0% vs 42.7%, p = 0.030) compared with nonsevere patients. Subgroup analysis demonstrated that MRGPRX2 was only significantly higher among treatment-naïve patients (severe: 58.15 ± 38.53, nonsevere: 25.91 ± 15.07; p = 0.034), rather than those on regular CSU medications (severe: 36.79 ± 22.98, nonsevere: 27.64 ± 17.15, p = 0.092). In contrast, differences in CCL2 did not reach statistical significance when analysing treatment-naïve patients (100.0% vs 58.1%, p = 0.283). Overall, serum MRGPX2 levels also showed significant correlation with CCL-2; but subgroup analysis revealed this correlation only remained significant among treatment-naïve patients as opposed to patients on regular CSU treatment (Figure 1 and https://osf.io/mz29q). Our study supports that both MRGPRX2 and CCL-2 may be potential biomarkers for CSU. We found that both serum markers were also strongly intercorrelated, but only among treatment-naïve patients. Similarly, MRGPRX2 was only significantly different among treatment-naïve patients, rather than those on regular CSU treatment. Alike other secreted substances, we postulate that medications used in the treatment of CSU (such as H1-antihistamines, mast cell stabilisers, anti-IgE biologics etc.) may interfere with mast cell degranulation/exocytosis of MRGPRX2-containing vesicles, therefore affecting measurable serum MRGPX2 levels among patients on treatment [9]. In contrast, CCL2 has been postulated to be a chemokine secreted by other cell types (such as monocytes) creating a proinflammatory environment in CSU and therefore may be less affected by medications [8]. There were several limitations to this study. Firstly, was its observational nature and patients were recruited on a consecutive basis, and there remains a possibility of ascertainment bias (e.g., patients with milder disease were more likely to be treatment-naïve). Secondly, as not all patient-reported outcome measures in traditional Chinese had been validated during recruitment, only UAS7 was included in analysis. Third, the cohort size was small and direct correlation between UAS7 or further subgroup analysis could not be performed (e.g., stratifying different treatment modalities, medical comorbidities or CSU subtypes). Fourth, all patients were ethnically Chinese and from a centre in Hong Kong which limits external. Similarly, no reference range was available for MRGPRX2 and there is possibility of inter-individual or -ethnic variability. These limitations highlight the need for further dedicated, prospective and multicentre studies on MRGPX2 and CCL2 among CSU patients. We propose that serum MRGPX2 and CCL-2 may be potential biomarkers reflecting CSU severity. It is important to note that, unlike CCL-2, MRGPRX2 may be more useful among treatment-naïve CSU patients (e.g., newly diagnosed CSU patients before treatment or after temporary cessation of medications) for more objective assessment and may also be used to indirectly measure adherence to treatment. The potential complimentary role of both these novel biomarkers warrants further study in larger, longitudinal studies which are currently underway. The author takes full responsibility for this article. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.