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Welcome to CE on ReachMD. This activity is provided by Global Learning Collaborative and is part of our IBD Masterclass curriculum.

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Dr. Odufalu:
Hello. My name is Dr. Florence-Damilola Odufalu. I'm a gastroenterologist at Keck School of Medicine of USC.

Inflammatory bowel disease is not a single pathway disorder but the result of a complex breakdown in immune regulation at the intestinal barrier. In the following animation, we will walk through the key pathophysiologic processes that drive chronic inflammation in IBD, highlighting where immune signaling becomes dysregulated.

Animation Voiceover:
Inflammatory bowel disease develops when genetic susceptibility and changes in the gut microbiome trigger a chronic, dysregulated immune response, leading to ongoing intestinal inflammation.

Genetic and acquired defects impair mucus production, antimicrobial peptide secretion, autophagy, and tight junction integrity. This leads to increased epithelial permeability, allowing microbial products to reach the underlying lamina propria.

The innate immune cells sense these signals through the pattern-recognition receptors, triggering the release of innate pro-inflammatory cytokines including TNF-α, interleukin-12 and -23.

These mediators further activate the local endothelium and generate chemokine gradients that recruit circulating innate immune cells.

At the same time, dendritic cells sample luminal antigens and migrate to mesenteric lymph nodes, where they present antigens to naïve CD4-positive T cells, initiating the adaptive immune response.

Depending on the cytokine environment, these T cells differentiate into specialized effector groups:

• In Crohn’s disease, the response is driven by Th1 and Th17 cells. Interleukin-12 drives Th1 cells to produce high levels of interferon-γ, while interleukin-23 induces Th17 differentiation.

• In ulcerative colitis, the response is frequently skewed toward Th2 and Th17 cells.

These effector cells then re-enter the circulation and home back to the intestine by using adhesion molecules and integrins that “dock” them to gut-associated vessels.

Within the lamina propria, these effector T cells become dominant cytokine producers.

At this stage, interleukin-23 amplifies pathogenic Th17 responses and drives the innate lymphoid cells 3 and 1 to produce additional cytokines, reinforcing local inflammation independent of antigen specificity.

Persistent inflammation activates the intestinal microvasculature, promoting ongoing immune cell recruitment and a self-sustaining inflammatory loop.

Dr. Odufalu:
As the animation shows, once inflammation becomes established, it creates a feed-forward cycle, cytokines recruit inflammatory cells, those cells produce more cytokines, and inflammation becomes locked into the intestinal wall, defining IBD as a chronic, self-sustaining disease process.

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