Mucosal mast cells (MMC) play a major role in allergic disease of the gut and in the
immune response to gastrointestinal nematodes where, in the mouse, their precursors
are recruited into the jejunum and migrate intraepithelially. There, they can be
identified as the mature phenotype by their expression of the MMC-specific
chymase, mouse mast cell protease-1 (mMCP-1).
Migration of other immune cells is regulated by adhesion to extracellular matrix
(ECM) proteins via expression of adhesion molecules such as integrins, and by
interactions with chemotactic molecules such as chemokines. Previous work with
other mast cell phenotypes suggests mast cells to be no exception to this regulatory
system, therefore the aim of this project was to investigate the role of integrins and
chemokines in mast cell migration.
Initial experiments analysed, using RT-PCR, expression of potential mast cell
chemoattractants from intestinal epithelium following infection of mice with the
nematode parasite, Nippostrongylus brasiliensis. Chemokines MlP-la, RANTES,
fractalkine and TECK, and cytokines SCF and TGF-Pi were constitutively expressed
from intestinal epithelium; and MCP-1 expression was detected only on days 7 and
14 post-infection, coinciding with intraepithelial migration of mast cells. Cultured
MMC and the CMT-93 intestinal epithelial cell line expressed some of these
molecules, suggesting epithelial cells or intraepithelial MMC as potential sources of
mast cell chemoattractants. Furthermore, expression of mRNA for chemokine
receptors including CCR1, CCR2, CCR5, CX3CR1 and CXCR4 was detected in
cultured MMC, possibly enabling migration towards chemokines expressed from
intestinal epithelium.
Adhesion of cultured MMC to ECM proteins was regulated by TGF-Pi, which also
regulates the mucosal phenotype, as shown by expression of mMCP-1. MMC
cultured with TGF-Pi adhered to laminin-1 via expression ofthe integrin a7pl, as
demonstrated by RT-PCR, flow cytometry and use of neutralising antibodies. MMC
cultured in the absence of TGF-Pi adhered to fibronectin and vitronectin but not
laminin-1, and did not express a7pi. Expression of a7pi integrin has not previously
been shown in a haemopoeitic cell and, as epithelial basement membranes are rich in
laminin, this integrin may aid migration and retention of MMC intraepithelially.
In conclusion, this work suggests expression of integrins and chemokine receptors by
MMC or their precursors, and of chemokines and cytokines by intestinal epithelium
as possible mechanisms regulating intraepithelial migration of MMC.
