Objective: Although it is known that the chemokines CXCL12 and CCL20 are expressed in the intestine, their contribution to lymphocyte homing has not been investigated in detail. The authors investigated whether the CXCL12-CXCR4 and CCL20-CCR6 systems are involved in T lymphocyte-endothelial interaction in microvessels of the small and large intestines.
Methods: Labeled lamina proprial lymphocytes (LPLs) were administered to mice, and their adhesion to microvessels of normal and TNF-alpha -induced inflamed intestinal mucosa was observed under an intravital microscope. Antibodies against CXCL12, CCL-20, or CCL-25 were administered prior to lymphocyte administration, and in some experiments CXCR4 or CCR6 on LPLs was desensitized with an excess amount of chemokine.
Results: LPLs adhered to microvessels of the ileum and colon, and TNF-alpha induced a significant accumulation at both sites. Blocking of the CXCL12-CXCR4 system significantly inhibited the LPL adhesion in the ileum and colon under both normal and TNF-alpha -treated conditions. However, blocking of the CCL20-CCR6 system significantly attenuated LPL adhesion only under a TNF-alpha -treated condition. There was an additive inhibitory effect on LPL adherence by CXCL12 and CCL20 blocking in TNF-alpha -induced inflamed intestines. There was also an additive function of the CCL25-CCR9 system in LPL accumulation in the small intestine.
Conclusion: Several chemokine systems may play significant roles cooperatively in vivo in LPL adherence to microvessels of intestinal mucosa.