Table 1.

Studies reporting on associations between serum/mucosal IgG4 and IBD.

Author, year	Study design	Serum or mucosal IgG4 levels	IBD pts (UC/CD)	Control group	Findings
Koutroumpakis et al. (42)	Observational, monocentric study	Serum IgG4 (Ref 9–89 mg/dL)	N: 1193 (788 CD, 405 UC)	/	High serum IgG4 levels in 61/1193 (5%); no difference between CD and UC Association with PSC No correlation with disease extent or severity
Faria et al. (43)	Cross-sectional study	Serum IgG4 > 140 mg/dL; Colon tissue ≥10 IgG4+ plasma cells per field	N: 56 (26 CD, 30 UC)	/	High serum IgG4 levels: 9 UC, 1 CD (p = 0,006); no association with disease activity 3/26 increased number of colon tissue IgG4 plasma cells, no correlation with high IgG4 in serum
Wang et al. (44)	Case–control study	Serum IgG4 > 1.50 g/L; Mucosal >10 IgG4+ plasma cells/HPF	N: 232 (28 CD, 104 UC)	45 healthy controls	Serum IgG4: no significant difference between groups (p > 0.05), elevated in 9.9% of IBD pts. Higher mucosal IgG4 in UC and CD In UC: correlation between high mucosal IgG4 and serum IgG4 levels, disease extension and severity Mucosal IgG4 significantly decreased after treatment with glucocorticosteroids
Raina et al. (45)	Retrospective	Mucosal >10 IgG4+ plasma cells/HPF in rectal biopsies	N: 54 (13 CD, 18 UC, 23 UC + PSC)	11 controls (aspecific diarrhea or microscopic colitis)	Significantly elevated in active UC and UC + PSC (p = 0.05). Not in CD, inactive UC, and controls
Şimşek et al. (46)	Retrospective	Mucosal >10 IgG4+ plasma cells/HPF	N: 72 (17 CD, 55 UC)	/	Significantly higher mucosal IgG4 in UC than CD (p = 0.01), correlation with disease activity in UC
Keyashian et al. (47)	Retrospective	Mucosal IgG4+ plasma cells/HPF in rectal biopsies	N: 134 UC	/	Significant association between IgG4-positive plasma cells and histological disease activity (p = 0.001) No association between IgG4 counts and clinical outcome
Navaneethan et al. (48)	Retrospective	Serum IgG4 > 112 mg/dL	N: 50 PSC pts. of which 42 had UC	/	High IgG4 in 10 PSC pts. (20%); not significantly associated with UC (p = 0.067), significantly associated with younger age at PSC diagnosis, backwash ileitis, UC flares, and reduced colectomy-free survival
Tavaghi et al. (49)	Retrospective	Serum IgG4-levels	N: 73 PSC pts. of which 51 had IBD	/	No significant difference between IgG4 serum levels in PSC pts. with or without IBD
Navaneethan et al. (50)	Prospective	Serum IgG4 ≥ 112 mg/dL	N: 124 UC pts. with symptomatic pouchitis	/	8% (10/124) high serum IgG4 No significant association with auto-immune disorders or PSC Significantly more chronic antibiotic-refractory pouchitis in high serum IgG4 (p = 0.03)
Virk et al. (51)	Retrospective	Mucosal >10 IgG4+ plasma cells/HPF in pretreatment colonic biopsies	N: 78 (50 UC, 38 CD)	/	Significantly higher mucosal IgG4 in UC than CD (p = 0.0001) Significant correlation with histological activity, but not with disease extent.

IBD, inflammatory bowel disease; CD, Crohn’s disease, UC, ulcerative colitis, pts, patients; PSC, primary sclerosing cholangitis; HPF, high power field.