Lymphoid aggregates in Crohn's colitis and mucosal immunity

Area of Science:

• Gastroenterology
• Immunology
• Colorectal Pathology

Background:

• Crohn's colitis involves increased lymphocytes and plasma cells in the colorectal mucosa.
• New lymphoid structures, including submucosal lymphoid aggregates (SLAs), form in Crohn's colitis.
• The cellular immune response within these structures in Crohn's colitis requires further investigation.

Purpose of the Study:

• To investigate the cellular immune response within mucosal lymphoid aggregates (MLAs), submucosal lymphoid aggregates (SLAs), and the lamina propria in Crohn's colitis.

Main Methods:

• Analysis of 59 colorectal biopsies/surgical specimens using MUM1 staining.
• MUM1 highlights activated T cells, committed B cells, and plasma cells (aT/cB/PC).
• Quantification of MUM1-positive cells per high-power field (HPF) in different colorectal compartments.

Main Results:

• A significantly lower number of MUM1-positive aT/cB/PC per HPF was observed in MLAs and SLAs in Crohn's colitis compared to controls.
• Conversely, a significantly higher number of MUM1-positive aT/cB/PC per HPF was found in the lamina propria in Crohn's colitis and other chronic colitis forms.
• The findings suggest a potential increase in MUM1-negative precursors in MLAs and SLAs in Crohn's colitis.

Conclusions:

• The distribution of activated immune cells differs between lymphoid structures and the lamina propria in Crohn's colitis.
• A paucity of activated immune cells in MLAs and SLAs may be due to precursor cell migration to the lamina propria.
• This migration likely supports the heightened immune response required by chronic inflammation in Crohn's colitis.