Association of Blastocystis subtype 3 with elevated IL-8–mediated inflammation in patients with irritable bowel syndrome

Background The role of Blastocystis in the pathophysiology of irritable bowel syndrome (IBS) remains controversial, with emerging evidence suggesting subtype-specific differences in pathogenicity. Interleukin-8 (IL-8), a key pro-inflammatory chemokine, has been implicated in mucosal immune activation in both IBS and parasitic infections. Objective This study aimed to investigate the association between Blastocystis subtypes and clinical manifestations of IBS, with a particular focus IL-8 as part of the systemic pro-inflammatory immune response associated with functional GIT disorders and intestinal infections. Methods In this cross-sectional study, 298 symptomatic patients attending a tertiary gastroenterology clinic were evaluated using Rome IV criteria for IBS diagnosis. Identification of Blastocystis in stool samples was done by direct microscopic examination. Subtype identification using PCR and subtype-specific sequence-tagged site primers were also performed. A balanced random selection was used to compare serum IL-8 levels between Blastocystis -positive IBS patients and an equal number of randomly selected Blastocystis -negative IBS patients. Clinical, biochemical, and demographic variables were analyzed in relation to infection status and subtype distribution. Results IBS was diagnosed in 197 out of 298 participants (66.1%), among whom 57 (28.9%) were positive for Blastocystis . Subtype analysis revealed a predominance of subtype (ST) 3 (86%), followed by ST1 (14%). Serum IL-8 levels were significantly higher in Blastocystis -infected IBS patients compared to non-infected controls (129.24 ± 56.28 vs. 26.28 ± 9.28 pg/mL, P < 0.001). Multivariate analysis identified younger age, diarrhea, and spring presentation as independent predictors of Blastocystis infection. Conclusions IBS is frequently associated with Blastocystis infection, particularly with subtype ST3. Serum levels of IL-8 are higher in Blastocystis -infected IBS patients as compared to uninfected ones. Statistical comparison between IL-8 levels in both subtype groups revealed no significant difference, despite the higher numerical values among the ST3 group. The potential aggravating effect of blastocystosis on IBS symptomatology and the relation between individual subtypes and the pro-inflammatory cytokine response require further mechanistic and longitudinal studies to clarify the causal relationship between Blastocystis subtypes and IBS pathogenesis. In addition, local inflammatory markers should be used to study local immune modulation and identify molecular effectors implicated in the pathogenesis of Blastocystis in IBS -infected patients.