Expression of neurotrophins and their receptors in human bone marrow

The expression of neurotrophins and their receptors, the low-affinity nerve growth factor receptor (p75(LNGFR)) and the Trk receptors (TrkA, TrkB, and TrkC), was investigated in human bone marrow from 16 weeks fetal age to ad ulthood. Using reverse transcription-polymerase chain reaction, all transcr ipts encoding for catalytic and truncated human TrkB or TrkC receptors were detected together with trkAI transcripts, whereas trkAII transcripts were found only in control nerve tissues. Transcripts for the homologue of the r at truncated TrkC(ic113) receptor were identified for the first time in hum an tissue. Stromal adventitial reticular cells were found immunoreactive fo r all neutrophin receptors. in contrast, hematopoietic cell types were not immunoreactive for p75(LNGFR) but showed immunoreactivity for one or severa l Trk receptors, TrkA immunoreactivity was found in immature erythroblasts. Catalytic TrkB immunoreactivity was observed in eosinophilic metamyelocyte s and polymorphonuclear cells. Truncated TrkB immunoreactivity was found in erythroblasts and megacaryocytes. Immunoreactivity for both catalytic and truncated TrkC receptor was observed in promyelocytes, myelocytes, some pol ymorphonuclear cells and megacaryocytes. Neutrophin transcript levels appea red higher at fetal than at adult stages, no variation in Trk family transc ript levels was observed. The local expression of neurotrophin genes sugges ts a wide range of paracrine and/or autocrine mode of action through their corresponding receptors within the bone marrow.