B1a lymphocytes in the rectal mucosa of ulcerative colitis patients

AIM: To assess B1a cell expression in the rectal mucosa of ulcerative colitis (UC) patients in comparison with healthy controls.METHODS: Rectal mucosa biopsies were collected from 15 UC patients and 17 healthy controls. CD5⁺ B cells were analysed by three colour flow cytometry from rectal mucosal samples after mechanical disaggregation by Medimachine^®. Immunohistochemical analysis of B and T lymphocytes was also performed. Correlations between, on the one hand, rectal B1a cell concentrations and, on the other, erythrocyte sedimentation rate and C-reactive protein levels and clinical, endoscopic and histological disease activity indices were evaluated.RESULTS: Rectal B-lymphocyte (CD19⁺/CD45⁺) rate and concentration were higher in UC patients compared with those in healthy controls (47.85% ± 3.12% vs 26.10% ± 3.40%, P = 0.001 and 501 ± 91 cells/mm² vs 117 ± 18 cells/mm², P < 0.001); Rectal B1a cell density (CD5⁺CD19⁺) was higher in UC patients than in healthy controls (85 ± 15 cells/mm² vs 31 ± 6.7 cells/mm², P = 0.009). Rectal B1a cell (CD5/CD19⁺) rate correlated inversely with endoscopic classification (Rs = -0.637, P < 0.05).CONCLUSION: B1a lymphocytes seem to be involved in the pathogenesis of UC, however, the role they play in its early phases and in disease activity, have yet to be defined.