ORIGINAL ARTICLE Clinical features of cytotoxic CD8+ T-lymphocyte deficiency in chronic rhinosinusitis patients: a demographic and functional study Nathalie Gabra 1, ∗ , Saud Alromaih, MD 2, ∗ , Leandra Mfuna Endam, MSc 3 , Rose Marie Brito, MSc 4 , Franc ¸ oise Larivi ` ere, MD, FRCPC 8 , Sawsan Al-Mot, MSc 3 , Franc ¸ oise LeDeist, MD, PhD 4,5,6 and Martin Desrosiers, MD, FRCSC 3,4,5,6,7,8 Background: Identification of Staphylococcus aureus intra- cellularly in chronic rhinosinusitis (CRS) suggests an under- lying cellular immunodeficiency. Supporting this, we have previously reported low CD8+ (cytotoxic) T-lymphocyte levels in a subpopulation of CRS patients and identified polymorphisms in the CD8A gene associated with CRS. In order to beer understand the role of low CD8+ in CRS, we wished to determine the phenotype for CRS/Low CD8+ in comparison to that of conventional CRS. Methods: Sixty-seven low CD8+ CRS patients identified during investigation of CRS were compared for demograph- ics, disease evolution, and bacteriology on endoscopic cul- ture were compared with an existing population of 480 pa- tients with CRS with nasal polyposis previously recruited for genetic association studies. Results: Mean level of CD8+ in the CRS/Low CD8+ population was 0.15 × 10 9 /L (range, 0.20–1.5 × 10 9 /L). There was no difference between both groups in terms of history of allergy, asthma, eczema, acetylsalicylic acid (ASA) intolerance or smoking. The bacteriology was simi- lar between both groups (S. aureus: CRS/Low CD8+: 35%; CRS 32%, p = 0.643). Evolution of disease was somewhat milder in CRS/Low CD8+, with fewer patients requiring surgery, and first surgery performed at a more advanced age. However, antibiotic use was higher in CRS/Low CD8+. Subgroup analysis restricted to CRS with nasal polypo- sis (CRSwNP)/Low CD8 or CRS without nasal polyposis (CRSsNP)/Low CD8 phenotypes did not substantially alter these results. Conclusion: Low CD8+ levels are oſten identified in CRS patients; however, these patients have disease remarkably similar to those with conventional CRS. This suggests that immune deficiency, whether systemic or locally mediated, is well tolerated and may be present in other forms in CRS. CRS patients with low CD8+ levels may possibly require antibacterial therapies as part of ongoing manage- ment. C  2014 ARS-AAOA, LLC. Key Words: Bacteriology; chronic rhinosinusitis; disease severity; immunodeficiency; rhinosinusitis; superantigen How to Cite this Article: Gabra N, Alromaih S, Mfuna Endam L, et al. Clinical features of cytotoxic CD8+ T-lymphocyte deficiency in chronic rhinosinusitis patients: a demographic and func- tional study. Int Forum Allergy Rhinol. 2014;4:495–501. T he lining of the paranasal sinuses represents a mucosal interface between the internal and external environ- 1 Faculty of Medicine, University of Montreal, Montreal, Quebec, Canada; 2 Department of Otolaryngology-Head and Neck Surgery, McGill University, Montreal, Quebec, Canada; 3 Centre de Recherche du Centre Hospitalier de l’Universit ´ e de Montr ´ eal (CRCHUM), Montreal, Quebec, Canada; 4 Centre Hospitalier Universitaire (CHU) Sainte-Justine, Research Center, Montreal, Quebec, Canada; 5 Department of Microbiology, Infectiology, and Immunology, University of Montreal, Montreal, Quebec, Canada; 6 Department of Pediatrics, University of Montreal, Montreal, Quebec, Canada; 7 Division of Otolaryngology-Head and Neck Surgery, Centre Hospitalier de l’Universit ´ e de Montr ´ eal (CHUM), Montreal, Quebec, Canada; 8 Department of Biochemistry, Centre Hospitalier de l’Universit ´ e de Montr ´ eal (CHUM) Correspondence to: Martin Desrosiers, MD, FRCSC, Centre Hospitalier de l’Universit ´ e de Montr ´ eal, H ˆ otel-Dieu, Pavillon Marie-Morin, local 4-423, 3840 ments where antigens and pathogens are encountered and cleared with a minimal inflammatory reaction. 1 However, in a considerable proportion of individuals, persistent in- flammation of the sinus mucosa, with intense cellular infil- trate and bacterial colonization occurs, resulting in chronic rhinosinusitis (CRS). Whereas current efforts attempt to understand the pathology of the disease by describing the immunologic rue St Urbain, Montr ´ eal, Qu ´ ebec H2W 1T8, Canada; e-mail: desrosiers_martin@hotmail.com ∗ N.G. and S.A. contributed equally to this work. Potential conflict of interest: None provided. Received: 11 August 2013; Revised: 4 January 2014; Accepted: 7 January 2014 DOI: 10.1002/alr.21313 View this article online at wileyonlinelibrary.com. 495 International Forum of Allergy & Rhinology, Vol. 4, No. 6, June 2014