Differential expression of Thy-1 on the various components of connective tissue of rat nerve during postnatal development.

The glycoprotein Thy-1 is found on the surface of both neurons, and most fibroblasts, in tissue culture of embryonic or neonatal rat nervous tissue. In adult rat nerves, however, we find the antigen restricted in vivo to neurons and their axons (R. Morris, P. Barber, J. Beech, and G. Raisman, 1983, J. Neurocytol., 12, 1017-1039). We show here that this discrepancy is due to a loss of Thy-1 from neural connective tissue during postnatal development. Moreover, the different elements of connective tissue loose Thy-1 at different times. Epineurial fibroblasts, for instance, express Thy-1 for at least 2 weeks after endoneurial fibroblasts lack detectable antigen. As judged by their loss of Thy-1 antigen, therefore, the different components of neural connective tissue mature at different rates. One important practical implication of this is that Thy-1 cannot be used as a cell surface "marker" for all classes of fibroblasts in vitro. Unusual problems encountered in the immunohistochemical staining of Thy-1 on perineurium, but not on the other elements of the nerve, are also described.