Luminal CD4⁺ T cells penetrate gut epithelial monolayers and egress from lamina propria to blood circulation

Background & Aims: The egress of memory T cells from peripheral tissues, such as lung and skin, into the draining lymph nodes requires their expression of CC chemokine receptor 7 (CCR7). In the intestine, resident memory T cells in the intestinal lamina propria (LP) do not express CCR7, indicating that they are tissue bound and do not exit the intestine. Methods: We developed a cell transfer system, using rectal administration of lymphocytes to C57BL/6 mice. Lymphotoxin α-deficient mice were crossed with RAG-2^-/- (recombination-activating gene-2) mice to generate lymphotoxin α-deficient × RAG-2^-/- mice. Results: Severe combined immunodeficient (SCID) or RAG-2^-/- mice given rectal administration of splenic CD4⁺ T cells from normal mice developed colitis; the cells proliferated not only in the LP but also in spleen. SCID or RAG-2^-/- mice given rectal administrations of CD4⁺ T cells that expressed green fluorescent protein (GFP⁺CD4⁺ T cells) localized to the LP within 6 hours but were not found in the spleen until 24 hours after administration. Immunohistochemical and electron microscopic analyses detected CD4⁺ T cells in the intraepithelial space just 3 hours after intrarectal administration. However, neither CCR7 deficiency nor the sphingosine-1-phosphate receptor agonist Fingolimod impaired the egress of CD4⁺ T cells from LP to systemic circulation. Conclusions: CD4 ⁺ T cells not only penetrate from the luminal side of the intestine to the LP but also actively egress from the LP into the circulation. We developed a rectal administration system that might be used to further investigate cell trafficking in intestinal mucosa and to develop enema-based therapeutics for intestinal diseases.