Immunohistochemical localization of cysteine-rich intestinal protein in rat small intestine

Cysteine-rich intestinal protein (CRIP) is a LIM (cysteine-rich motif of leu-11, isl-1, and mec-3 genes) domain protein with a double zinc finger motif. The protein is abundantly expressed in the intestine, peritoneal macrophages, and peripheral blood mononuclear cells. The function of CRIP is not known. The purpose of this study was to determine the cellular distribution of CRIP in rat intestine, as an initial step toward eventual determination of a function. Immunohistochemical and immunogold labeling electron microscopy using a purified polyclonal rabbit antibody to a synthetic peptide representing a zinc finger domain of rat CRIP were carried out on sections of rat duodenum. Western blotting was used to detect signal specificity of the antibodies. These immunohistochemical and electron microscopy studies showed particularly high abundance of CRIP in the cytoplasmic granules of Paneth cells of the intestine. Some evidence of CRIP expression was also found in cells of the villus tip, but abundance was less than that found in the Paneth cells. The localization of CRIP in Paneth cells and its presence in mononuclear cells suggests that CRIP may be involved in host defense mechanisms and/or tissue differentiation/remodeling processes common to these cell types.