Proc. Nati. Acad. Sci. USA Vol. 89, pp. 778-781, January 1992 Immunology Immunosuppression in the definitive and intermediate hosts of the human parasite mansoni by release of immunoactive neuropeptides (neuroimmunomodulation/conformational changes/neutral endopeptidase/parasite neuropeptides/-parasite interactions) ODILE DUVAUX-MIRET*, GEORGE B. STEFANOt, ERIC M. SMITHS, COLETTE Dissous*, AND ANDRE CAPRON* *Centre d'Immunologie et de Biologie Parasitaire, Institut National de la Sante et de la Recherche M6dicale Unit6 167, Centre National de la Recherche Scientifique 624, Institut Pasteur, 59019 Lille Cedex, France; tMultidisciplinary Center for the Study of Aging, State University of New York, Old Westbury, NY 11568; and tDepartments of Microbiology and Psychiatry and Behavioral Sciences, University of Texas Medical Branch, Galveston, TX 77550 Communicated by Berta Scharrer, October 14, 1991

ABSTRACT Evidence supporting the concept that the nuclear cells (PMN) (2, 3) as well as the migration of parasitic trematode Schistosoma mansoni may escape immune invertebrate immunocytes (4). Recently, it also was found reactions from its vertebrate (man) or invertebrate (the fresh- that ACTH can exert the same immunosuppressive cellular water snail glabrata) hosts by using signal mol- effects through conversion into a-MSH by means of neutral ecules it has in common with these hosts was obtained by the endopeptidase 24.11 (NEP or "enkephalinase"), since the following experiments. The presence of immunoactive proop- enzyme is present on the surface of both mammalian PMN iomelanocortin (POMC)-derived peptides [corticotropin and invertebrate immunocytes (5, 6). (ACTH), 13-endorphin] in, and their release from, S. mansoni The aim ofthe present study was to test our hypothesis that was demonstrated. Coincubation of adult worms with human S. mansoni may take advantage of these immunoactive polymorphonuclear leukocytes or B. glabrata immunocytes led phylogenetically conserved molecules to interfere with the to the appearance of a-melanotropin (MSH) in the medium. normal immune response ofthe host. More precisely, the role The conclusion that this a-MSH resulted from conversion ofthe of the parasite POMC-derived peptides in immunosuppres- parasite ACTH by neutral endopeptidase 24.11 (NEP) present sion in the definitive host (man) and in the intermediate host on these cells was supported by the fact that the a-MSH level (the ) has been ex- in the medium was markedly reduced by addition ofthe specific amined. NEP inhibitor phosphoramidon. This interpretation is substan- tiated by the fact that no conversion was observed in compa- MATERIALS AND METHODS rable tests with human monocytes, which exhibit no NEP activity. a-MSH has the capacity to inactivate formerly active Parasites and Hosts. A Puerto Rican strain of S. mansoni immunocytes not only from the definitive host (man, hamster) was maintained in the laboratory in the hamster Mesocricetus but also from the intermediate host (B. glabrata), as determined auratus and in the intermediate host B. glabrata. Adult by microscopic computer-assisted examination of conforma- worms were collected by portal perfusion of 40-day-infected tional POMC-derived have been detected in hamsters and were washed thoroughly with minimal essential changes. peptides medium (Eagle's), containing penicillin at 100 units/ml and B. glabrata hemolymph 2, 10, and 24 days after by S. streptomycin at 50 ,ug/ml (MEM-PS) at 37°C. For RIAs, the mansoni miracidia. Immunocytes from infected snails were worms were sedimented, drained, and lyophilized. found to be inactivated, and this inactivation was prevented by Incubations ofworms were carried out at 37°C in MEM-PS antibodies directed against ACTH and a-MSH. The immuno- in a 5% CO2 atmosphere for 2 hr at a concentration of50 pairs active P-endorphin released from S. mansoni does not appear of worms (male plus female) per ml in culture plates. Coin- to be subject to enzymatic conversion. Since it is active at lower cubation with human PMN was performed under the same concentrations, it may be used for distant signalng. conditions in the presence of 3 x 106 human PMN per ml, prepared from healthy donors (7), in Linbro microwell tissue Thus far the scarcity of information on the mechanisms culture plates (Flow Laboratories). The enzyme inhibitors enabling the survival ofSchistosoma mansoni in its definitive bestatin and phosphoramidon were added as indicated at a and intermediate hosts has stood in the way ofthe eradication final concentration of 0.1 mM. of , a major human parasitic . In this B. glabrata hemolymph and hemocytes were withdrawn report we provide evidence indicating that the interaction through the snail shell with a microsyringe (26 gauge needle between parasite and host involves the dispatch by the /2 inch long) in the pericardium from either healthy or parasite of the same signal molecules as those found in the infected specimens. Hemocytes were pelleted, if necessary, host into the immediate vicinity of the , thus by 500 x g centrifugation and resuspended in phosphate- interfering with the host immune function. buffered saline. Hemolymph supernatant, after a 15-min We have recently demonstrated the presence of proopi- centrifugation at 10,000 x g, was collected and pooled from omelanocortin (POMC)-derived peptides [immunoactive cor- 10-15 age-matched snails. ticotropin (adrenocorticotropic hormone, ACTH), a-mela- Hamster PMN were prepared as described elsewhere (7). notropin (melanocyte-stimulating hormone, a-MSH), and Structural Analysis of Immunocytes. Changes in conforma- ,B-endorphin] in all stages of the life cycle of S. mansoni (1). tion of hamster and human PMN or B. glabrata hemocytes This finding is highly significant because a-MSH has been based on measurements of cell area and cell perimeter were shown to counteract the inflammatory action of interleukin 1 determined by the use of American Innovision (San Diego) and tumor necrosis factor by inhibiting human polymorpho- Abbreviations: POMC, proopiomelanocortin; PMN, polymorphonu- The publication costs of this article were defrayed in part by page charge clear leukocytes; ACTH, corticotropin (adrenocorticotropic hor- payment. This article must therefore be hereby marked "advertisement" mone); MSH, melanotropin (melanocyte-stimulating hormone); in accordance with 18 U.S.C. §1734 solely to indicate this fact. NEP, neutral endopeptidase 24.11. 778 Downloaded by guest on September 28, 2021 Immunology: Duvaux-Miret et al. Proc. Natl. Acad. Sci. USA 89 (1992) 779 form-factor calculations as described in detail elsewhere (8). resulted from de novo synthesis and release from the adult Briefly, the form factor is equal to Ac/AT = [LT/Lc]2, where worm. AT is the area of a circle with the same perimeter as that of Furthermore, under these conditions a-MSH was detected the given cell and LT is the perimeter ofa circle with the same only within the adult worms, not in the incubation medium. area as that of the given cell; Ac and Lc represent the actual This may be due to the absence of release of this compound. area and perimeter of the cell. The computer-assisted image Since Smith et al. (6) demonstrated that NEP may be in- and video analysis system were the same as previously volved in the conversion of ACTH to an a-MSH-like mole- described (9). The immunocytes were prepared and treated as cule, the parasite ACTH-like molecule was tested for its noted in detail elsewhere (5, 9). In the cardiac aspiration of potential to be converted to the antiinflammatory peptide immunocytes from infected molluscs the cells were mixed on a-MSH by coincubating adult worms (for 2 hr) with human the slide with saline and the antibodies (anti-ACTH and PMN, which contain NEP on their surface (5) (Table 1, anti-MSH) were diluted to 1:100. Incubations under the in Experiment B). This time was chosen on the basis of results vitro conditions were for 40 min, based on previous experi- of the study by Smith et al. (6). Under these conditions, the ments (6, 10). Statistical analysis was carried out by means of ACTH-like material was no longer present and immunoactive Student's t test. The mean value from 10 separate trials, each a-MSH was detected in the incubation medium. The role of trial representing a single cell measurement, was averaged NEP in this conversion was ascertained by use ofthe specific with three additional mean values similarly obtained to NEP inhibitor phosphoramidon, which significantly reduced provide the value for each point on the various graphs. the amount of immunoactive a-MSH in the medium. By to RIA contrast, bestatin, an aminopeptidase inhibitor that does not RIA. All samples were lyophilized to dryness prior affect NEP activity, did not modify the levels ofACTH in the and examined as previously noted in detail (11). Briefly, medium. These results strongly suggest that human PMN ACTH, MSH, and f-endorphin levels were determined by have the ability to convert the parasite immunoactive ACTH use of commercially available kits (Incstar, Stillwater, MN). to immunoactive a-MSH. This was further substantiated by The sensitivity of the ACTH and MSH assay was approxi- performing the same incubation with B. glabrata immuno- mately 15 pg/ml, and that for P3-endorphin was 5 pg/ml. cytes, which also contain NEP on their surface. This exper- Using peptide standards, we found less than 0.1% cross- iment gave basically the same results (not shown). On the reactivity for the inappropriate peptide in the assays. Ly- contrary, when adult worms were coincubated with human ophilized hemolymph from infected snails or incubation monocytes, which are devoid of NEP, no a-MSH was found medium of worms was assayed according to the kits' instruc- (data not shown). The amount of the parasite immunoactive tions. All three assays are based on the experimental sample ACTH was increased in the presence of phosphoramidon, binding to specific antibodies adsorbed to a test tube, thereby since the worm continued to release it and it was not inhibiting the binding of 1251-labeled peptide standards. Each degraded. Bestatin also increased the amount of ACTH-like assay needed 50-100 jA of sample. Bound radiolabeled tracer material, an observation that remains unexplained; it may be was quantitated with a y counter. Values in pg/ml were indicative of a multienzymatic pathway (6). It should also be extrapolated from the standard curve, based on the percent noted that immunoactive /3-endorphin levels were not af- inhibition of binding of radiolabeled tracer. fected by the peptidase inhibitors used during immunocyte Materials. Synthetic peptides (ACTH, a-MSH, 13-MSH, incubations, indicating that this peptide appears to be resis- ,3-endorphin) were purchased from Peninsula Laboratories. tant to proteolytic attack by membrane-bound peptidases. Bestatin and phosphoramidon were purchased from Sigma. Cells from both mammalian hosts (human and M. auratus) Antibodies used to reverse hemocyte activation were ob- as well as from the intermediate mollusc host B. glabrata tained from Incstar. were tested for their ability to respond to a- and (3-MSH (Fig. 1). The degree of activation of the immunocytes was quan- RESULTS tified by calculation of the form-factor, which is inversely related to their perimeter. The lower the form-factor, the Definitive Host. ACTH-like and P-endorphin-like sub- more ameboid the cell shape (9). In this assay, the cells stances were detected in the incubation medium of adult responded to a- or B-MSH by an increase in form-factor. The worms incubated in MEM-PS and assayed for POMC- sensitivity of the vertebrate PMN was higher than that of the derived peptides (Table 1, Experiment A). Interestingly, their mollusc immunocytes (effective concentration 10-9 and 10-7 level in the medium was relatively higher than that found in M, respectively), as had already been described for human the parasites, suggesting that the amount found in the medium PMN and Mytilus edulis immunocytes (4, 6). Within an hour, the presence ofACTH in the immunocyte incubation medium Table 1. RIA of ACTH, a-MSH, and 3-endorphin in S. mansoni did not affect the cells' activation, since conversion requires adult worms and incubation medium more than 1 hr, as noted elsewhere (6). Sample ACTH a-MSH 13-Endorphin Intermediate Host. For the determination of the activity of these peptides in the intermediate host, ACTH, a-MSH, and Experiment A, peptide conc. in pmol/g wet wt B. Parasites 0.2% ± 0.07 1.840 ± 0.11 0.222 ± 0.12 ,3-endorphin were assayed in the hemolymph of infected ± ND 0.740 ± 0.13 glabrata at different developmental stages of the sporocysts Medium 1.265 0.32 All were in infected Experiment B, peptide conc. in fmol/ml and cercaria (Table 2). peptides detected ± 2.1 ± 0.9 snails, whereas none were found in noninfected controls. PMN ND 29.7 0.0 were 30 hr PMN + phos. 5.0 ± 1.3 22.0 ± 0.0 2.0 ± 0.7 High levels of a-MSH detected approximately ± ± ± after infection (day 2), corresponding to the formation of the PMN + bestatin 4.1 0.1 36.0 5.1 1.3 0.1 mother sporocyst, which escapes encapsulation (12). At day Experiment A: Adult worms (1-1.5 g wet weight) were incubated 10, when all daughter sporocysts have completed their mi- in MEM-PS at 370C for 2 hr in a 5% CO2 atmosphere (50 couples per gration into the digestive gland (12), all three peptides were ml). Peptides were assayed either in the worms prior to incubation in the at when mature or in the incubation medium after incubation. Experiment B: Fifty present hemolymph. Finally, day 24, pairs ofadult worms were incubated in the presence of3 x 106 human cercariae are liberated into the water, only immunoactive PMN in 1 ml of MEM-PS with no additions or with phosphoramidon ACTH could be detected in the hemolymph. Peptide con- (phos.) or bestatin at 0.1 mM. Incubation medium was then assayed centrations in hemolymph ranged between 10-12 and 10-10 for the considered peptides after lyophilization. All values are M, an order of magnitude lower than that effective in immu- expressed as mean ± SEM. ND, not detectable. nosuppression. We believe this reflects a higher concentra- Downloaded by guest on September 28, 2021 780 Immunology: Duvaux-Miret et al. Proc. Natl. Acad. Sci. USA 89 (1992) A Table 2. Radioimmunoassay of ACTH, a-MSH, and /-endorphin in the hemolymph of S. mansoni-infected snails 0.800 \P)t<0.01 Peptide conc., fmol/ml 'I- _-6-A P)0.05 Sample ACTH a-MSH .3-Endorphin 0.600 Day 2 3.5 ± 0.0 66.0 ± 18.0 2.3 ± 0.5 O\A Day 10 4.3 ± 0.8 39.3 ± 0.39 2.0 ± 0.5 0.400 C, ..I\ A A Day 24 22.2 ± 4.8 ND ND Control ND ND ND 0.200 *-* Control active cells A mixture of hemocytes and hemolymph from control or infected A-A uMSH B. glabrata was centrifuged at 10,000 x g for 10 min, and the resulting EI-E #MSH supernatant was lyophilized and assayed. Ten to 15 different snails 0.000 that were age-matched and had been infected simultaneously were 3 4 5 6 7 8 9 10 11 12 13 14 15 taken for each measurement. Infestation occurred at 8 a.m. on day 1, and all samples were withdrawn at 4 p.m. on the corresponding a) a, B days. Results are expressed as mean ± SEM; ND, not detectable. a' 0.800 DISCUSSION In the we evidence S. mansoni la P)010___ present study, provide that as 0.600 a. releases at least two POMC-derived peptides under physio- x logical conditions: ACTH and P-endorphin, which have the potential to regulate the host immune function. These pep- x 0.400 tides, in effect, mask the worm from the host immunosur- *llance. In the definitive host the presence of adult worms 0 0.200 *-* Control active cells can be tolerated for decades, presumably because S. mansoni A -A aMSH is able to suppress immunoresponsiveness. Several addi- .-Cu 0-0DMSH tional effects of ACTH and f3-endorphin may be relevant in E 0.000 0 3 4 5 6 7 8 9 10 11 12 13 14 15 schistosomiasis. ACTH is known to suppress interferon LL (IFN) production by T lymphocytes (13) and also to inhibit C IFN activation of macrophages (14). Inhibition of IFN pro- duction after oviposition in experimental mouse schistoso- 0.800 >|A miasis has been recently reported (15, 16). Moreover, immu- A '>0.01 nosuppression of the host(s) has been demonstrated also in the case of protozoan and to some extent of helminthic 0.600 lA (17). This can be achieved by evading the host immune response by molecular mimicry, phyletic conver- * gence, or other mechanisms (18, 19). Some parasite-derived 0.400 ** A molecules have been shown to interfere directly with the host metabolic and/or immune activities for protozoans (20), 0.200 cestodes (21), (22), and trematodes (23). A-A aMSH The parasite ACTH can be converted to a-MSH by NEP *-* Control active cells from human, hamster, and invertebrate immunocytes (5, 6). 0.000 This is highly significant, since a-MSH inhibits adherence and locomotory activity of PMN, monocytes, and inverte- -log10o [peptide conc. (M)] brate immunocytes (3, 4). Since the parasite ACTH can be converted to a-MSH, we surmise that it is also involved in the FIG. 1. Immunosuppressive effects of a- and 3-MSH on spon- limitation of PMN and peripheral blood mononuclear cell taneously asctive human PMN (A), hamster PMN (B), and B. glabrata adherence to adult worms, especially in their immediate immunocytes Hu). immunocytes were incuoatea witn tne peptiues for 1 hr. Controls consisted of immunocytes treated with physiolog- 0.900 ical saline. Variation for all mean values was not greater than 6%. Statistical analysis by Student's t test notes the point of significant O 0~ difference between round and ameboid cells (SD = +0.12) as the 0.800 result of drug. AK ts0 0.700 A * tion at the immediate cellular level, compatible with an A v inhibitory immune action in the vicinity of the sporocysts. 0 0.600 Interestingly, the experiment reported in Fig. 2 indirectly U- 0-C Control A demonstrates the participation of these POMC-derived fac- *- * AB ACTH tors in the inhibition of immunocytes. Immunocytes were 0.500 A-A AB-aMSH freshly withdrawn from 14-day infected snails and immedi- A-A AB-ACTH & -oMSH with 0.400 ately incubated antibodies directed against ACTH or 70 a-MSH. All cells were inactivated (rounded) at the beginning 0 10 20 30 40 50 60 of incubation (form factor 0.800). Both antibodies reversed Time, min hemocyte inhibition to form factor 0.500 typical of activated cells. A plausible explanation is that immunoresponsive FIG. 2. Reversal of inhibition of immunocytes obtained from S. hemocytes are inhibited by the addition of both peptides, mansoni infected B. glabrata by antibodies (AB) directed against ACTH or a-MSH. The antibodies were diluted to a 1:100 with snail ACTH being converted into a-MSH by NEP which is present saline and added to the in vitro incubation medium, consisting of snail on the surface of B. glabrata immunocytes. In this experi- hemolymph. Immunocytes in this medium without the antibodies ment, only 37% ± 5% of the cells responded to antibodies, continued to be rounded for at least 1 hr. Variation for all mean values suggesting that other inhibitory factors might be operating. was not greater than 6%. Downloaded by guest on September 28, 2021 Immunology: Duvaux-Miret et al. Proc. Natl. Acad. Sci. USA 89 (1992) 781

vicinity. These peptides may be further implicated in the Cadet of the Old Westbury Neuroscience Institute for excellent absence of cytolytic action by cytotoxic T lymphocytes, technical assistance. We thank Blandine Baratte and Han Vorng for although adult worms acquire determinants ofthe host major technical help and Dr. Jean-Yves Cesbron for scientific advice. We histocompatibility complex on their tegument (24). also express our gratitude to Dr. Berta Scharrer for thoughtful We have demonstrated previously that the parasite P3-en- comments and discussions. We acknowledge the following grant dorphin is very similar to human P-endorphin-(1-31) (1, 25). support: Alcohol, Drug Abuse, and Mental Health Administration stimulates chemotaxis of MARC 17138, National Science Foundation INT 8803664, National p8-Endorphin monocytes and PMN Institute on Drug Abuse 47392, and the Research Foundation/State (4, 9), but it inhibits the production of a T-cell chemotactic University of New York (to G.B.S.). E.M.S. was supported by factor (26), augments suppressor T-cell activity (27), and National Institute of Diabetes and Digestive and Kidney enhances natural cytotoxicity (28). Concerning humoral re- Grant 41034-01, Office ofNaval Research Grant N0014-89-J1%2, and sponses, it inhibits antibody production (11) and B-lympho- the John Sealy Memorial Foundation. cyte conversion into immunoglobulin-secreting cells (29). Clearly, parasite 18-endorphin might be partly implicated in 1. Duvaux-Miret, O., Dissous, C., Gautron, J. P., Pattoux, E., Kor- the up-regulation of the immune response toward schisto- don, C. & Capron, A. (1990) New Biol. 2, 93-99. 2. Robertson, B., Dostal, K. & Daynes, R. A. (1988) J. Immunol. 140, somula, and also in some immunosuppressive effects favor- 4300-4307. ing parasite adaptation. 83-Endorphin has been shown to 3. Van Epps, D. E. & Mason, M. M. (1990) in Comparative Neu- resist degradation better than ACTH or a-MSH and to be ropeptide Pharmacology, eds. Florey, E. & Stefano, G. B. more potent, since it has the potential to initiate activity at (Manchester Univ., Manchester, U.K.). 10-10 M (30). These characteristics lead us to surmise that 4. Stefano, G. B., Smith, D. E., Smith, E. M. & Hughes, T. K. (1992) may have an action that occurs at some distance in Molluscan Neurobiology, eds. Boer, H. & ter Maat, A. (Elsevier/ ,8-endorphin North Holland, Amsterdam), in press. from the site of parasitic infestation. 5. Shipp, M. A., Stefano, G. B., D'Adamio, L., Switzer, S. N., How- Concerning the intermediate host, the freshwater snail B. ard, F. D., Sinisterra, J., Scharrer, B. & Reinherz, E. (1990) Nature glabrata, the present work demonstrates that a population of (London) 347, 394-396. its hemocytes responds to ACTH and MSH as do other 6. Smith, E. M., Hughes, T. K., Jr., Hashemi, F. & Stefano, G. B. invertebrate immunocytes (4, 6). Moreover, a-MSH, and to (1992) Proc. Natl. Acad. Sci. USA 89, 782-786. a lesser extent ACTH and could be detected in 7. Boyum, A. (1968) Scand. J. Clin. Lab. Invest. Suppl. 21, 31-50. 13-endorphin, 8. Schon, C., Torre-Bueno, J. & Stefano, G. B. (1991) Adv. Neuroim- the hemolymph of snails infected by S. mansoni. Whether munol. 3, in press. these peptides are of parasitic or of molluscan origin remains 9. Stefano, G. B., Cadet, P. & Scharrer, B. (1989) Proc. Natl. Acad. to be determined. However, the consistent failure to detect Sci. USA 86, 6307-6311. them in hemolymph of control suggests that, at least 10. Stefano, G. B., Shipp, M. A. & Scharrer, B. (1991) J. Neuroim- in part, the parasite does contribute either directly or indi- munol. 31, 97-103. to the detectable levels found in 11. Woloski, B. M. R. N. J., Smith, E. M., Meyer, W. J., III, Fuller, rectly infected animals. G. M. & Blalock, E. J. (1985) Science 230, 1035-1037. Penetration of noncompatible snails by S. mansoni miracidia 12. Capron, A., Deblock, S., Biguet, J., Clay, A., Adenis, L. & Vernes, results in rapid encapsulation and killing ofthe larvae. On the A. (1965) Bull. Organ. Mond. Sante 32, 755-778. contrary, in a compatible snail, encapsulation is inhibited 13. Johnson, H. M., Torres, B. A., Smith, E. M., Dion, L. D. & within the first hours following penetration of the miracidium Blalock, J. E. (1984) J. Immunol. 132, 246-251. and depends mostly on the inhibition of the of the 14. Koff, W. C. & Dunegan, M. A. (1985) J. Immunol. 135, 350-354. capacity 15. Pearce, E. J., Caspar, P., Grzych, J. M., Lewis, F. A. & Sher, A. snail immunocytes to emit pseudopodia and adhere to the (1991) J. &p. Med. 173, 159-166. sporocyst surface (19), which could potentially be due to 16. Grzych, J. M., Pearce, E. J., Cheever, A., Caulada, Z. A., Caspar, parasite a-MSH. Interestingly, Lie et al. (31) have demon- P., Heiny, S., Lewis, F. & Sher, A. (1991) J. Immunol. 146, strated that circulating hemocytes from recently infected 1322-1327. snails retain their capacity for phagocytosis or response to 17. Dessaint, J. P. & Capron, A. (1992) in Immunology and Molecular certain stimuli in the infected state. We feel that the of Biology ofParasitic Infections, eds. Warren, K. S. & Agabian, N. report (Blackwell, Cambridge, MA), 3rd Ed., in press. Lie et al. (31) describes the physiological state of these cells 18. Capron, A. & Dessaint, J. P. (1989) Immunol. Rev. 112, 27-48. in the entire snail rather than in the immediate vicinity of the 19. Bayne, C. J. & Yoshino, T. P. (1989) Am. Zool. 29, 399-407. parasite. Furthermore, this is in accordance with the low 20. Ackerman, S. B. & Seed, J. R. (1976) Experientia 32, 645-650. concentrations of circulating peptides that we observed. 21. Phares, C. K. & Watts, D. J. (1988) J. Parasitol. 74, 896-898. Another possible mechanism in this interaction may con- 22. Faubert, G. M. & Tanner, C. E. (1974) Immunology 27, 501-505. sist of liberation the 23. Mazingue, C., Walker, C., Domzig, W., Capron, A., DeWeck, A. peptide by snail immunocytes in the & Stadler, B. M. (1987) Int. Arch. Allergy Appl. Immunol. 83, vicinity of the sporocyst. Supporting this hypothesis is the 12-18. presence of ACTH and /8-endorphin in immunocytes of the 24. Sher, A., Hall, B. F. & Vadas, M. A. (1978) J. Exp. Med. 148, closely related mollusc Planorbarius corneus (32). Several 46-52. reports have described an increase of the number of circu- 25. Duvaux-Miret, 0. & Capron, A. (1992) Ann. N.Y. Acad. Sci., in lating hemocytes in mollusc trematodes press. by (33, 26. Brown, S. L. & Van Epps, D. E. (1985) J. Immunol. 134, 3384- 34). Inhibition of immunocyte locomotion by a-MSH has 3390. been shown to result in an increase of circulating cells as a 27. McCain, H. W., Lamster, I. B. & Bilotta, J. (1986) J. Immunop- result of inhibition of margination (35). harmacol. 8, 443-446. Our results constitute an example of molecular mimicry by 28. Froehlich, C. J. & Bankhurst, A. D. (1984) Life Sci. 35, 261-265. which parasites use phylogenetically conserved molecules to 29. Morgan, E. L., McClurg, M. C. & Janda, J. A. (1990) J. Neuroim- interfere with the host The results of the munol. 28, 209-217. response. present 30. Stefano, G. B. (1989) Prog. Neurobiol. 33, 149-159. work demonstrate the ability of schistosomes to release 31. Lie, K. J., Heyneman, D. & Jeong, K. H. (1976) J. Parasitol. 62, ACTH and 3-endorphin which can (i) act directly on immune 608-615. cells of both the definitive and the intermediate hosts and (ii) 32. Ottaviani, E., Petraglia, F., Montagnani, G., Gossarizza, A., Monti, be converted into immunosuppressive substances by NEP, D. & Franceschi, C. (1990) Regul. Pept. 27, 1-9. an enzyme present on the surface of the same cells. This 33. Abdul-Salam, J. M. & Michelson, E. H. (1980)J. Invert. Pathol. 35, constitutes with nor- 241-248. phenomenon parasitic interference the 34. Van der Knaap, W. P. W., Meuleman, E. A. & Sminia, T. (1987) mal autoimmunoregulatory activity of the host. Parasitol. Res. 73, 57-65. 35. Stefano, G. B., Zhao, X., Bailey, D., Metlay, M. & Leung, M. We express our gratitude to Ms. Lisa A. Mallozzi and Mr. Patrick (1989) J. Neuroimmunol. 21, 67-74. Downloaded by guest on September 28, 2021