Pii: S0145-305x(00)00047-1

It is widely accepted that all organisms have processes that maintain their state of health. Failure of these processes, such as those involving the naturally occurring antibacterial peptides, may lead to pathological events. Recent results demonstrate that these peptides, such as peptide B, appear in invertebrates and vertebrates (including humans) immediately after tissue trauma, and maintain themselves for long durations (over 4 h). Their degradation products lead to other in ̄ammatory peptides, such as Met-enkephalin-Arg-Phe. These newly described antibacterial peptides, which are released and not induced, are present on neuropeptide precursors such as proenkephalin. This is a new ®eld of research, in that the same protein contains proposed neuropeptides, antibacterial peptides, and immune stimulatory peptides. The focus of this review is to describe how the proenkephalin derived peptides participate in immune processes. q 2001 Elsevier Science Ltd. All rights reserved.