Gamma interferon-like immunoreactive material in rat neurons: evidence against a close relationship to gamma interferon.

Gamma interferon is a potent immunoregulatory peptide produced by activated lymphocytes. Recently, a gamma interferon-like immunoreactive molecule has been demonstrated immunohistochemically in subpopulations of rat neurons. We have now further characterized this molecule. Western blot analysis of spinal ganglia homogenates revealed a single 60,000 mol. wt band that was immunoreactive with monoclonal antibody DB1 directed against rat gamma interferon. A polyclonal antiserum and the monoclonal antibodies DB10 and DB12 failed to detect this band although all antibodies were able to label the major 18,000 mol. wt band of recombinant gamma interferon on the same blots. The 60,000 mol. wt band was selectively present in homogenates from primary sensory and sympathetic ganglia but was absent from the central nervous system and other peripheral organs, corresponding to the reported immunocytochemical distribution of gamma interferon-like immunoreactivity. The 60,000 mol. wt protein does not appear to be glycosylated. It could not be solubilized by detergents such as Triton X-100 and it co-purified with cytoskeleton-enriched preparations. At the nucleic acid level, Northern blot analysis using probes specific for rat gamma interferon mRNA failed to detect specific mRNA in rat spinal ganglia, whereas a strong 1.2 kb signal was detected in activated spleen cells. Functionally, gamma interferon-like immunoreactive material is strongly induced in superior cervical ganglion neurons after preganglionic axotomy of the sympathetic chain, but remains constant or slightly decreases in L5 spinal ganglion neurons after sciatic nerve transection. In contrast, major histocompatibility complex antigens are strongly induced on non-neuronal cells in both systems. We conclude that the neuronal gamma interferon-like immunoreactive material is clearly distinct from lymphocyte-derived gamma interferon and might not be involved in the control of major histocompatibility complex expression on glial cells.