Lymphopenia in Chronic Spontaneous Urticaria is Linked to Basopenia and Eosinopenia

Circulating blood numbers of lymphocytes in chronic spontaneous urticaria (CSU) have not been given sufficient attention. Histopathological analysis of wheals in CSU has demonstrated an increased number of mast cells (MCs) and a perivascular infiltrate of T lymphocytes along with variable numbers of basophils, eosinophils, monocytes and neutrophils [1]. Grattan et al. reported lower blood lymphocyte counts in CSU patients than in healthy controls [2].

Autoimmune CSU (aiCSU), in which MCs and basophils are activated by immunoglobulin G (IgG) autoantibodies against the high-affinity receptor FcεRI for immunoglobulin E (IgE) or against IgE, is characterised by high disease activity and poor response to standard treatments [3]. An early attempt to define aiCSU using three criteria (i.e. a positive basophil activation test or histamine release, a positive autologous serum skin test [ASST] and a positive immunoassay for IgG anti-FcεRI or IgE), which are not usually available in clinical practice, did not incorporate clinical features now known to be important [4]. Several recently described features of aiCSU, such as blood basopenia and eosinopenia, high levels of IgG against thyroid peroxidase (anti-TPO) and low total serum IgE levels [3, 4], can assist in identifying patients with aiCSU, but there is still a need for additional parameters. We aimed to search for new routinely available markers of aiCSU in a substantial cohort of patients.

This study involved 300 CSU patients aged 17 years and older (68% female; mean age 45.0 years, SD 15.6 years), all assessed by the same dermatologist at Clinic Golnik. CSU was diagnosed clinically [5]. Exclusion criteria included prior omalizumab treatment, systemic glucocorticosteroid treatment within 7 days of venesection, predominant chronic inducible urticaria, wheals persisting more than 48 h and bradykinin-mediated angioedema. Data on demographics, patient history and laboratory tests were obtained at the initial visit as part of routine clinical care, based on the guidelines and clinical suspicion of comorbidities. The following laboratory tests were done at the Clinic Golnik laboratory: automated complete blood count (CBC) with differential (n = 300; Sysmex XN 3100, Sysmex), C-reactive protein (CRP; n = 292), total serum IgE (n = 149), anti-TPO (n = 184), antinuclear antibodies (ANA; n = 86) and IgG against complement component C1q (anti-C1q; n = 81). All patients were followed up for a minimum of 3 months, and responses to standard treatments were assessed. Uncontrolled CSU was defined as the Urticaria Control Test (UCT) score of 0–11 [5]. The study was approved by the Slovenian National Medical Ethics Committee (KME78/09/14). These data were systematically collected from patients' charts with their consent, in a retrospective manner, and analysed using IBM SPSS version 25. Fisher's exact test, Student's t-test and the Mann–Whitney test were used, and Spearman's rho rank correlation coefficient (r) was calculated. A p value of <0.05 was considered statistically significant.

Lymphopenia (<1.5 cells × 10⁹/L), detected in 26% (77 of 300) of patients, was associated with lower counts of basophils (p < 0.001), eosinophils (p = 0.007), monocytes (p = 0.002) and platelets (p < 0.001), as well as higher rates of basopenia (<0.01 cells × 10⁹/L; p = 0.002) and eosinopenia (<0.05 cells × 10⁹/L; p = 0.002). Additionally, patients with lymphopenia had higher rates of high anti-TPO than those with normal lymphocyte counts, but the difference was not statistically significant (p = 0.080). Lymphopenia was not associated with a poor response to second-generation H₁-antihistamines (sgAHs) or omalizumab (Table 1). Lymphocyte counts were weakly correlated with basophils (r = 0.26, p < 0.001), eosinophils (r = 0.25, p < 0.001), monocytes (r = 0.27, p < 0.001), neutrophils (r = 0.23, p < 0.001) and platelets (r = 0.29, p < 0.001).

Our research is the first to report a connection between lymphopenia, basopenia and eosinopenia, along with lower monocyte and platelet counts. Positive correlations among lymphocyte, basophil, eosinophil and monocyte counts suggest a simultaneous reduction in these cell types in the blood. Most CSU patients are believed to exhibit Type 2 inflammation that involves the fine-tuning of the immune response associated with a distinct set of cytokines released by T helper 2 (T_H2) cells, B cells, MCs, basophils and eosinophils [6]. High levels of Type 2 cytokines, including IL-4, IL-13 and IL-31, have been demonstrated in the lesional skin and/or blood of CSU patients [1, 6]. We hypothesise that lymphopenia in the blood may also reflect migration of lymphocytes (i.e. T cells and B cells) from the bloodstream into skin lesions, similar to the migration of basophils and eosinophils suggested in cases of basopenia and eosinopenia [3].

The rates of basopenia (10%) and eosinopenia (16%) were relatively comparable to those reported by Kolkhir et al. (14% and 10%, respectively) [7]. This analysis confirmed previous observations that eosinopenia is associated with basopenia and low total IgE, and basopenia with poor responses to sgAHs and omalizumab [7]. We also linked basopenia with lower lymphocyte counts (p = 0.002) and high anti-C1q (p = 0.031) (Table 1).

High anti-C1q levels were detected in 27% (22 of 81) of our patients, which is higher than the estimated 5% prevalence in healthy individuals. These antibodies are sensitive indicators for hypocomplementemic urticarial vasculitis syndrome [8]. Garmendia et al. reported significantly higher levels of anti-C1q in 34 CSU patients than in 30 healthy controls (p < 0.001) and suggested that these antibodies may represent a marker of aiCSU [9]. Our research is the first to identify associations between anti-C1q and basopenia, supporting this hypothesis.

While this study has strengths, including a large sample size and data homogeneity, it also has limitations, such as its retrospective design, the absence of a control group and potential inaccuracies in automated CBC analysis. We confirmed and extended previous findings about the immunological complexity of CSU. Lymphopenia could serve as an additional marker for aiCSU, but further research is needed to better understand its clinical implications. Additional information is available in the following repository: https://zenodo.org/records/12553443.

M. Bizjak designed the study, clinically evaluated the patients, collected the data, performed the statistical analysis, interpreted the data and wrote the paper, incorporating critical input from all authors. M. Košnik contributed to patient recruitment. All authors contributed to the interpretation of the data and literature review. All authors have approved the final version of the manuscript.

The study was approved by the Slovenian National Medical Ethics Committee (KME78/09/14). It was conducted in accordance with the Declaration of Helsinki, and informed consent was obtained from all participants.

M. Bizjak is or recently was a speaker and/or advisor for Novartis, outside the submitted work. R. Asero has recently been speaker and/or advisor for Novartis, GSK, Astra Zeneca, Lofarma, Hal Allergy, Smart Practice, Allergy Therapeutics, Menarini, Malesci, all outside the submitted work. E. Kocatürk is or recently was a speaker and/or advisor for Novartis, Menarini, LaRoche Posey, Sanofi and Bayer, all outside the submitted work. Ana M. Giménez-Arnau is or recently was a speaker and/or advisor for and has received research funding or participated in research from Almirall, Amgen, AstraZeneca, Avene, Celldex, Escient Pharmaceutials, Genentech, GSK, Instituto Carlos III- FEDER, Leo Pharma, Menarini, Mitsubishi Tanabe Pharma, Novartis, Sanofi–Regeneron, Servier, Thermo Fisher Scientific and Uriach Pharma/Neucor, outside the submitted work. M. Maurer is or recently was a speaker and/or advisor for and/or has received research funding from Astria, Allakos, Alnylam, Amgen, Aralez, ArgenX, AstraZeneca, BioCryst, Blueprint, Celldex, Centogene, CSL Behring, Dyax, FAES, Genentech, GIInnovation, GSK, Innate Pharma, Kalvista, Kyowa Kirin, Leo Pharma, Lilly, Menarini, Moxie, Novartis, Pfizer, Pharming, Pharvaris, Roche, Sanofi/Regeneron, Shire/Takeda, Third Harmonic Bio, UCB and Uriach, all outside the submitted work. M. Košnik has no relevant conflicts of interest to declare.