LIPOPOLYSACCHARIDE INDUCES PROENKEPHALIN GENE-EXPRESSION IN RAT LYMPH-NODES AND ADRENAL-GLANDS

The proenkephalin gene encodes a family of neuropeptides that was orig inally identified in brain tissue and adrenal glands. Recently, it was shown that proenkephalin is also expressed in cultured lymphoid cells . To elucidate the physiological significance of this expression, we e xamined the in vivo expression of proenkephalin in lymphoid tissues. W e show here that exposing rats to the endotoxin lipopolysaccharide ind uces an intense and transient expression of proenkephalin in adrenal g lands and lymph nodes. By using combined in situ hybridization and imm unohistochemistry on tissue slices, we identified proenkephalin expres sion in macrophages located within the lymph nodes and in chromaffin c ells within the adrenal glands. This in vivo expression of proenkephal in was enhanced by adrenaline. The present observations demonstrate th at the immune system is a site of significant expression of proenkepha lin and provide a basis for neuroimmune interactions.