Two-photon analysis of calcium signals in T lymphocytes of intact lamina propria from human intestine

Lamina propria (LP) T cells of the human intestinal mucosa usually do not develop systemic immune responses despite permanent exposure to foreign antigens. The mechanisms maintaining this hyporeactivity in the normal gut are poorly understood. It is, at present, not clear what role the microenvironment of the mucosa plays for low T cell reactivity and in the pathogenesis of mucosal inflammation. Despite the importance of cytosolic Ca2+ signals for T lymphocyte activation, intracellular Ca2+ concentration measurements have so far only been performed in dissociated T cells, following disruption of the microenvironment. We used two-photon technology to measure Ca2+ signals in identified T lymphocytes within the intact mucosa to minimize impact on tissue integrity while preserving the cellular microenvironment. We show that Ca2+ signals in LP T cells correlate with the hyporeactivity of T cells in the intestinal immune system and furthermore link Ca2+ signals with inflammatory bowel disease. Our data implicate that Ca2+ signals in LP T cells do not depend on the microenvironment of the intact mucosa, since they are very similar to Ca2+ signals in dissociated LP T cells.