C57BL/6 Mouse Primary Small Intestinal Fibroblasts from Cell Biologics are isolated from the Small Intestinal tissues of pathogen-free laboratory mice and grown in gelatin pre-coated tissue culture flask with Cell Biologics’ Complete Growth Medium. Cells at passage 2-3 are harvested from flasks and cryo-preserved in vials. Each vial contains 0.5x106 cells per ml and is delivered frozen. C57BL/6 Mouse Primary Small Intestinal Fibroblasts are characterized by their spindle morphology and immunofluorescence staining with anti-FSP1/S100A4 (Millipore USA) antibody. These cells are negative for bacteria, yeast, fungi, and mycoplasma and can be expanded for 3-5 passages at a split ratio of 1:2 under the cell culture conditions specified by Cell Biologics. Repeated freezing and thawing of cells are not recommended.