CD34(+) cells in human intestine are fibroblasts adjacent to, but distinctfrom, interstitial cells of Cajal

Interstitial cells of Cajal (ICC) generate the pacemaker component of the g ut and play important roles in the control of gut motility. The tyrosine ki nase receptor Kit is an established marker for ICC. Recently, it has been r eported that immunoreactivity for the sialomucin CD34 may be present on ICC in human intestine. Gastrointestinal stromal tumors express both Kit and C D34, suggesting that these tumors may derive from ICC. We characterized the distribution of CD34 immunoreactivity at the cellular level in the normal human gut, using double immunofluorescence immunohistochemistry and confoca l microscopy. CD34 immunoreactivity identified previously unrecognized cell s closely adjacent to, but distinct from, the Kit immunoreactive ICC. These CD34 immunoreactive cells expressed the fibroblast marker prolyl 4-hydroxy lase-whereas ICC did not-and were also distinct from smooth muscle cells, g lial cells, and macrophages. In the human gut, CD34 immunoreactivity is not expressed by ICC but by a population of fibroblasts, likely corresponding to the "fibroblast-like cells" described in previous ultrastructural studie s. Our findings also challenge the hypothesis that stromal tumors originate from ICC.