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Source created 2026-08-25 · updated 2026-08-25
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ASCRS Ch43 - Inflammatory Bowel Disease Pathobiology

Chapter 43, "Inflammatory Bowel Disease: Pathobiology," ASCRS Textbook of Colon and Rectal Surgery, 4th edition. Authors: Benjamin D. Shogan and Pokala Ravi Kiran. Book pp. 743–750 (title page through References).

Textbook reference chapter (not primary literature), Part IV/benign-and-miscellaneous material. Mainly a reconciliation chapter: substantially deepens the existing Inflammatory Bowel Disease page's previously thin "Epidemiology and etiology" section with a full host-factors/microbiome/environmental-factors framework, and resolves a long-flagged open item on Ileal Pouch-Anal Anastomosis (IPAA) by supplying its first Pouchitis section. Also extends (not resolves) an existing cross-source discrepancy between Crohn Disease and Colonic Physiology over the direction of Bacteroidetes change in IBD dysbiosis.

Structure

  • Introduction: IBD pathophysiology framed as multifactorial — genetic, environmental, microbial, and immune factors interacting (Fig 43.1); rising incidence in developing/urbanizing countries as key evidence for environmental factors' importance.
  • Host Factors — Genetics: population/twin-study heritability data (8–10× relative risk, 50% MZ-twin CD concordance vs. <15% UC); polygenic architecture (>hundreds of loci, each low-effect); monogenic early-onset/very-early-onset CD (IL-10 signaling defects, T-cell dysfunction); named genes (NOD2/CARD15 — first identified CD gene, 2001; IRGM, ATG16L1 — autophagy; IL23R, PTPN2 — autoimmune-disease overlap); epigenetics (DNA methylation, histone modification, miRNA regulation).
  • Host Factors — Immunity: mucosal immune system architecture (epithelium/Paneth cells, lamina propria macrophages/dendritic cells, T/B cells/Peyer's patches); Th1/Th17/Th2/Th3/Th9/Treg balance; UC-as-Th2 vs. CD-as-Th1 framing (with caveat re: oversimplification); detailed cytokine roles (IL-17/IL-22, IFN-γ, IL-2/STAT4, IL-1/IL-8/IL-6, IL-12, IL-23, TNF-α).
  • Intestinal Microbiome: dysbiosis pattern (decreased diversity; increased Fusobacterium/ Proteobacteria; decreased Firmicutes/Bacteroidetes); Table 43.1 candidate organisms by bacteria/virus/fungus category; virome (Caudovirales, Synechococcus phage S, Retroviridae) and mycobiome (S. cerevisiae, C. albicans, Basidiomycota) changes, independent of bacterial composition; oxygen-tension theory of dysbiosis; antibiotic-exposure risk data (case-control, cohort, and meta-analysis evidence, strongest for CD).
  • Environmental Factors: urbanization (Fig 43.2 incidence trends in Turkey/Punjab/Brazil/Hong Kong before/after 2000; rural-upbringing protective effect); smoking (divergent CD-risk-increasing vs. UC-protective effect, meta-analysis ORs, CYP2A6/GSTP1 genetic modulation); NSAIDs (dose- dependent mixed evidence, 2018 systematic review/meta-analysis finding no significant association overall); diet (Cochrane review uncertainty, meat vs. fruit/vegetable associations).
  • Pouchitis Pathobiology: incidence (~50% UC vs. rare/never FAP — genetic-component evidence); IL-1 receptor-antagonist SNP (+2018, RR 3.1); NOD2 mutation association with severe pouchitis; TLR2/4 upregulation; defensin-1/defensin-5 expression changes; fecal-stasis-driven colonic metaplasia of pouch mucosa; microbiome shift (decreased Bacteroidetes, increased Proteobacteria vs. FAP-pouch controls); IL-12 pathway/complement-cascade transcriptomic signature.

Open items / gaps

  • Every named study (Carter's IL-1 SNP finding, Sehgal's NOD2 finding, McLaughlin's pouchitis- microbiome finding, the antibiotic-exposure meta-analysis, the NSAID systematic review, the smoking meta-analyses) is cited at the textbook/secondary level only — see Inflammatory Bowel Disease's and Ileal Pouch-Anal Anastomosis (IPAA)'s own Open items for what would be highest-value to independently ingest first.
  • The Bacteroidetes direction-of-change discrepancy between Crohn Disease (Sabiston-sourced) and Colonic Physiology (ASCRS Ch. 2) is not resolved by this chapter — it independently agrees with the Sabiston/Crohn Disease direction, making it 2-against-1, but cohort/methodology heterogeneity in IBD microbiome literature means this is not treated as dispositive.
  • Chapter 44 ("IBD Diagnosis and Evaluation," Brar MS, MacRae H) begins next — its opening page (book p.751) was visible in this read but not yet ingested.