Antibodies against the amino-terminal portion of pro-enkephalin inhibit DNA synthesis in human peripheral mononuclear cells

Abstract

Pro-enkephalin (PENK) mRNA and PENK-derived peptides have been reported in lymphocytes, monocytes, and macrophages. Met-enkephalin (ME) and/or synenkephalin (SYN)-containing peptides are produced and released by human peripheral blood lymphocytes (HPBL) activated with phytohemagglutinin (PHA). Furthermore, SYN (PENK 1–70) was cleaved to low-molecular-mass peptides in HPBL. In this work we studied the effect of a mouse monoclonal antibody (mAb) and a rabbit antiserum (pAb) against the C-terminal portion of SYN on DNA synthesis in PHA-activated HPBL. [ 3H]Thymidine incorporation into HPBL incubated with 0.1 μg/ml of PHA was tested in the presence of different concentrations of mAb immunoglobulin (Ig) G or different dilutions of pAb. mAb induced a concentration-dependent decrease of [ 3H]thymidine incorporation into HPBL: 7%, 19%, 28%, and 35% of inhibition was observed with 0.1, 1, 1.5, and 2 μg IgG, respectively, reaching values of 65% with 10 μg IgG. Similarly, pAb dilutions of 1 500 , 1 1000 , 1 2000 and 1 4000 inhibited DNA synthesis by 63%, 61%, 43%, and 30%, respectively. The inhibitory effect of mAb and pAb was specific since it was not produced by non-immune mouse IgG or several non-immune rabbit sera and was completely reversed by 1 μM of the synthetic peptide |Tyr 63](syn 63–70) synenkephalin. These results suggest that low-molecular-mass SYN-derived peptides released by PHA-activated HPBL may participate in the proliferative response of these cells. This is further evidence that the non-opioid portion of PENK—that is, SYN-derived peptides—may be involved in tissue development.