282 Journal of Leukocyte Biology Volume 51, March 1992 Synthetic hexapeptides derived from the transmembrane envelope proteins of retroviruses suppress N-formylpeptide--induced monocyte polarization Robert A.J. Oostendorp Wim M. M. Schaaper1 Jacob Post,t Rob H. Meloen,t and Rik J. Scheper* 5Department of Pathology, Free University Hospital, Amsterdam and tLaboratory of Molecular Immunology, Central Veterinary Institute, Lelystad, The Netherlands Abstract: Retroviral infections are frequently associated with immunosuppression. Retroviral transmembrane envelope proteins (TM proteins) play an important role in this phenomenon. CKS-1 7, a synthetic heptadecapep- tide, represents the immunosuppressive site of these retroviral TM proteins. Here we report on the further delineation of this immunosuppressive site using CKS-1 7-derived hexapeptides. The N-formyl-methionyl- leucyl-phenylalanine-induced monocyte polarization as- say was used throughout this study because this monocyte function has been shown to be highly sensitive to TM protein pl5E-related immunosuppression. We found that in addition to CKS-1 7 one CKS-1 7-derived hexapeptide, LDLLFL, reversibly inhibited monocyte polarization, with 50% inhibitory concentrations of 20 and 2 tM respectively. LDLLFL-mediated inhibition was sequence specific because the reverse peptide LFLLDL and scram- bled peptides were not inhibitory. Hexapeptides cor- responding to LDLLFL, but derived from various retroviruses other than murine leukemia virus, also in- hibited monocyte polarization. Peptides most homolo- gous to LDLLFL - LDILFL (feline leukemia virus) and LDLLFW (human T lymphotropic virus types I and II)- were the most potent inhibitors. Peptides homolo- gous to primate and human endogenous proviruses were not suppressive. LDLLFL and some of its homologues also inhibited polarization of neutrophilic granulocytes. These findings lend further support to the view that con- served retroviral TM protein-related peptides can play an important role in suppression of inflammatory cell function as encountered in retrovirus-associated immuno- suppression. J. Leukoc. Biol. 51: 282-288; 1992. Key Words: retroviruses immunosuppression synthetic pep- tides monocyte function INTRODUCTION Immunosuppression is frequently encountered in cancer pa- tients [6, 40], human immunodeficiency virus (HIV)-sero- positive people [43], and patients with chronic inflammatory diseases [30, 44]. Defective monocyte responses to chemotac- tic stimuli are most frequently noted. It has been demon- strated that such immunosuppression may result from cir- culating factors antigenically related to retroviral transmembrane envelope (TM) proteins [3, 6, 41, 43, 44]. Both human and murine tumors were found to secrete low- molecular-weight factors (LMWFs) with immunosuppres- sive properties [38]. Antibodies directed against the pl5E TM protein ofmurine leukemia virus (MuLV) abolished the immunosuppression induced by preparations of LMWF derived from human tumors. Retroviral pl5E was found t be immunosuppressive [38], and a recombinant protein der ived from a murine retroviral pl5E gene [35, 37] showed similar activity. Tumor-derived pl5E-related LMWFs hay been shown to depress delayed-type hypersensitivity reac tions in mice [27, 42]. These results led to the hypothesis tha pl5E-related LMWFs may facilitate tumor progression [38] TM proteins from various retroviruses share homology ii a sequence of 26 amino acids [7]. CKS-17, a synthetic hep tadecapeptide derived from this consensus sequence, in hibited many different in vitro lymphocyte [5, 14, 21, 23, 24 29], natural killer (NK) cell [18], and monocyte [17, 20] func tions. CKS-17-induced immunosuppression was als demonstrated in vivo [26]. More importantly, CKS-V homologues derived from the amino acid sequences of HIV-: and human T lymphotropic virus type I (HTLV-I) showe similar in vitro suppressive activities [4, 36]. These result favor the view that the CKS-17-like sequences represent major immunosuppressive site of the retroviral TM proteins Considering the importance of the CKS-17 domain ii pl5E-related immunosuppression, we decided to investigati this sequence further and find out whether CKS-17-relate immunosuppression might reside in even smaller peptides For this purpose we synthesized a series of overlapping pep tides covering the complete sequence of CKS-17. This so called PEPSCAN approach has proved successful ii delineating antibody binding sites [13] as well as T cell epi topes [48]. We used hexapeptides because it had previousl been shown that retrovirus-related hexapeptides could sup press T lymphocyte responses to interleukin 2 (IL-2) [46] Abbreviations: BaEV, baboon endogenous virus; BSA, bovine serum al bumin; DAE, 1,2-diaminoethane; DAH, 1,6-diaminohexane; DMSC dimethyl sulfoxide; FeLV, feline leukemia virus; IMLP, N-formyl methionyl-leucyl-phenylalanine; HERV, human endogenous retrovirus HIV, human immunodeficiency virus; HPLC, high-performance liqufi chromatography; HSA, human serum albumin; HTLV, human T lym photropic virus; IC50, 50% inhibitory concentration; IL-2, interleukin 2 KLH, keyhole limpet hemocyanin; LMWF, low-molecular-weight factor, M BS, maleimido-benzoyl-hydroxy-succinimide ester; MuLV, murine leuke mia virus; NK cell, natural killer cell; PBS, phosphate-buffered saline; RE\ A, reticuloendotheliosis-associated virus; RSV, Rous sarcoma virus; T1 protein, transmembrane envelope protein. Throughout this paper one-lette codes representing L-amino acids are used: A, alanine; D, aspartic acid; E glutamic acid; F, phenylalanine; G, glycine; I, isoleucine; K, lysine; L, let. cine; P, proline; N, asparagine; Q, glutamine; R, arginine; T, threonine; ‘v tryptophan; and Y, tyrosine. Reprint requests: R.A.J. Oostendorp, Department of Pathology, Fred University Hospital, Dr Boelelaan 1117. 1081 HV Amsterdam, The Nether lands. Received April 1, 1991; accepted July 24, 1991.