RECRUITMENT OF TISSUE RESIDENT CELLS TO HYDROGEL COMPOSITES - IN-VIVORESPONSE TO IMPLANT MATERIALS

A model of local cellular recruitment was established using hydrogel m atrices composed of alginate implanted subcutaneously into mice. Cells which trafficked to the matrix blocks were recovered and characterize d for surface phenotype using iluorescently labelled antibodies and fl ow cytometry (fluorescence activated cell sorting). Temporal informati on of the differential recruitment of cells was determined. The basic pattern of recruitment in response to the hydrogels was established an d mimicked that seen in a local inflammatory response. Neutrophils (PM N) were rapidly recruited (1 d) followed by macrophages and lymphocyte s (1-3 d). Cell surface phenotype studies included the determination o f CD3(+), CD4(+) and CD8(+) cells, Mac-1(+) cells, and immunoglobulin bearing cells. Microscopic analysis revealed numerous activated PMNs a nd monocyte derived foamy macrophages. Fluorescence immunocytochemistr y of frozen sections of the block revealed that macrophages, CD3(+) an d natural killer tells were all recruited to the interior of the block . Ultrastructural analysis (transmission electron microscopy) showed h ighly activated macrophages, with abundant rough endoplasmic reticulum and secretory vesicles. Cells which remained on the surface of the ma trix block were CD44 positive migratory cells. Electron microscopic ev idence showed foamy macrophages with a varying degree of involvement w ith the hydrogel material. Surface scanning electron microscopy reveal ed numerous fibroblast-like cells coating the surface of the block. We suggest that these methods may be used to address the inflammatory re sponse elicited with a variety of implanted materials such as hydrogel s, silicones, ceramics and metals. Furthermore, this model has been us eful in determining cellular responses to cytokines and growth factors under similar conditions.