BRAIN MACROPHAGES STIMULATE NEURITE GROWTH AND REGENERATION BY SECRETING THROMBOSPONDIN

The presence of macrophages in the developing or lesioned central nerv ous system (CNS) led us to study the influence of these cells on neuro nal growth. Macrophages were isolated from embryonic rat brain and we observed that factors released in vitro by these cells stimulate neuri te growth and regeneration of cultured CNS neurons. This effect was in hibited by antibodies directed against thrombospondin, an extracellula r matrix protein that we found to be synthesized and released by brain macrophages. Immunodetection of thrombospondin in the adult rat brain lesioned by kainic acid confirmed the production of this protein by b rain macrophages and indicated an early intraparenchymal accumulation of thrombospondin following injury. These results suggest that brain m acrophages contribute actively to neurite growth or regeneration durin g the development or in pathological contexts. (C) 1994 Wiley-Liss, In c.