Over 250,000 Americans are severely and permanently disabled due to acute spinal cord injuries (SCI). There currently is no therapy for promoting recovery of neurological function in chronic stages of SCI. The proposed study will test the central hypothesis that macrophages/microglia express matrix molecules that inhibit axonal outgrowth after SCI, and that the blockade of these putative inhibitory molecules will augment axonal regeneration. To challenge this hypothesis, the following Specific Aims will be addressed: 1) Determine the cellular source of CSPG proteoglycan expression using in situ hybridization and immunolabelling, and whether the inhibition of proteoglycan synthesis by application of the proteoglycan inhibitor beta-D- xyloside enhances axonal outgrowth after SCI; 2) Determine using semi-quantitative PCR whether macrophages treated with growth factors and cytokines modulate their expression of CSPGs in vitro; and 3) Determine whether grafts of fibroblasts genetically modified to express and secrete augmented amounts of inhibitory cytokines (e.g., interleukin 10 or other substances identified in Aims 2) will reduce the deposition of ECM molecules and promote axonal repair after SCI. Here, transgenic cellular delivery, immunolabeling, in situ hybridization and neuroanatomical tracing will be used.