Mem Inst Oswaldo Cruz, Rio de Janeiro, 92(5) Sep/Oct 1997
Differential Regulation of Granuloma Size and Hepatic Fibrosis in Schistosome Infections
Biomedical Research Institute, 12111 Parklawn Drive, Rockville, MD 20852 USA and Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, MD 20892-0425 USA
Granuloma size is the variable most frequently used to evaluate the immunopathogenesis of schistosome infections. However, hepatic fibrosis is at the least an equally relevant variable. Hepatic fibrosis and the size of circumoval granulomas are frequently dissociated in experimental murineu00a0Schistosoma mansoniu00a0andu00a0S. japonicumu00a0infections. Virtually nothing is known of the immunoregulation of schistosomal hepatic fibrosis. This review notes many of the studies which have found discrepancies in granuloma volume and hepatic fibrosis, attempts to put them in perspective and to evaluate different methods of calculating changes in collagen synthesis or content.
Differential Regulation of Granuloma Size and Hepatic Fibrosis in Schistosome Infections
In experimental schistosomiasis the degree of hepatic fibrosis often correlates with volume of hepatic granulomas, but there are numerous exceptions to this and the regulation of hepatic fibrosis and granuloma size are clearly at least partly independent.
It is clear that when comparing granuloma size and fibrosis that one should consider only those situations in which the duration of infection is the same in the groups being considered and in which only newly formed granulomas are measured, i.e. reactions around eggs containing mature, viable embryos.
It is less clear how one should quantify fibrosis. We have generally used the total increase above normal levels of hepatic collagen (determined as the increase in hydroxyproline per liver per egg). This gives a measure of the cumulative increase in total collagen (synthesis minus destruction) at any given time point, but different time points cannot be rigorously compared and rates of synthesis and destruction at specific times after infection are not determined. Collagen synthetic rates should give a better picture at any given moment, but one does not generally know the rate of collagen destruction at that moment. Even if the level of collagenases is known, should one in any case consider constitutive or latent collagenases, besides needing to consider at least type I and type III collagenases?
The frequent dissociation of granuloma size and collagen content or synthetic rates is evident in the Table. I find the interpretation difficult when granulomas decrease in size and the collagen or synthetic rate per g granuloma does not change, i.e. the collagen or synthetic enzymes in the granulomas are perhaps decreased but compacted into a smaller volume (Fig.). However, when the granulomas remain the same size and the collagen and synthetic rates per g granuloma decrease (Olds et al. 1989) or when different treatments have different effects (Olds & Kresina 1989), the results seem unequivocal. Similarly the results seem clearly interpretable when total hepatic collagen is considered in relation to egg numbers.
There are dissociations between granuloma size and fibrosis in addition to the treatments and comparisons noted in the Table. For example, in Schistosoma mansoni-infected mice granuloma volume does not change with intensity of infection (expressed as worm pairs or total liver eggs) while the fibrosis per egg decreases as infection intensity increases (Cheever 1986).
We know nothing of the kinetics of collagen deposition in relation to granuloma size in humans. We do know that in many cases of "active" Symmers' fibrosis that downregulatory anti-idiotypic T cells are absent and proliferation of peripheral blood mononuclear cells is greater than that in asymptomatic hepato-intestinal cases (Montesano et al. 1990). Similar anti-idiotypic T cells downregulate the size of in vitro granulomas formed around schistosome eggs by PMBC of infected patients (Parra et al. 1991). Obviously, it will be important to have surrogate variables of hepatic fibrosis and collagenolysis to follow in infected humans. Past studies suggest that serum procollagen III (Zwingenberger et al. 1988, Mincis et al. 1990, Fayol et al 1991, Shahin et al. 1992) or other serum precursors (Tanabe et al. 1989, Parise & Rosa 1992, Shahin et al. 1995) or in vitro responses of liver from infected patients (Dunn et al. 1979, Monteiro & Borojevic 1995) may be of interest in this regard. Collagen production by in vitro granulomas (Parra et al. 1991) has apparently not yet been examined.
The examples cited above and in the Table indicate that granuloma size and hepatic fibrosis are frequently regulated independently. The factors relevant to immune-modulation of granuloma size include CD8+ suppressor effector cells, CD4+ suppressor inducer and effector cells, macrophages, cross-regulation of Th1 and Th2 cells, anti-idiotypic antibodies (S. japonicum) and anti-idiotypic t cells (S. mansoni and S. japonicum). Immunoregulation of schistosomal hepatic fibrosis has been less examined and might affect pathways involved in collagen synthesis, cross-linking or collagenase activity. All of these pathways determining granuloma size and fibrosis are presumably affected by the balance of cytokines which may affect reaction size and fibrosis in different ways or to different degrees. For example, cytokines affecting cell recruitment might be expected to affect primarily the size of granulomas. Some treatments noted in the Table, i.e. anti-IL-4 treatment (Cheever et al. 1994), may act directly on enzymes affecting collagen (Postlewaite et al. 1992) as well as through immunoregulatory pathways.
Cheever AW 1986. The intensity of experimental schistosome infections modulates hepatic pathology. Am J Trop Med Hyg35: 124-133.
Cheever AW, Duvall RH, Hallack Jr TA 1984. Differences in hepatic fibrosis and granuloma size in several strains of mice infected with Schistosoma japonicum. Am J Trop Med Hyg33: 602-607.
Cheever AW, Duvall RH, Hallack Jr TA, Minker RG, Malley JD, Malley KG 1987. Variation of hepatic fibrosis and granuloma size among mouse strains infected with Schistosoma mansoni. Am J Trop Med Hyg37: 85-97.
Cheever AW, Finkelman FD, Caspar P, Heiny S, Macedonia JG, Sher A 1992. Treatment with anti-IL-2 antibodies reduces hepatic pathology and eosinophilia in Schistosoma mansoni-infected mice while selectively inhibiting T cell IL-5 production. J Immunol148: 3244-3248.
Cheever AW, Finkelman FD, Cox TM 1995. Anti-interleukin-4 treatment diminishes secretion of Th2 cytokines and inhibits hepatic fibrosis in murine schistosomiasis japonica. Parasite Immunol17: 103-109.
Cheever AW, Xu Y, Sher A, Finkelman FD, Cox TM, Macedonia JG 1993. Schistosoma japonicum-infected mice show reduced hepatic fibrosis and eosinophilia and selective inhibition of IL-5 secretion by CD4+ cells after treatment with anti-IL-2 antibodies. Infect Immunity61: 1288-1292.
Cheever AW, Williams ME, Wynn TA, Finkelman FD, Seder RA, Cox TM, Hieny S, Caspar P, Sher A 1994. Anti-IL-4 treatment of Schistosoma mansoni-infected mice inhibits development of T cells and non-B, non-T cells expressing Th2 cytokines while decreasing egg-induced hepatic fibrosis. J Immunol153: 753-759.
Dunn MA, Kamel R, Kamel IA, Biempica I, El Kholy A, Hait PK, Rojkind M, Warren KS, Mahmoud AAF 1979. Liver collagen synthesis in schistosomiasis mansoni. Gastroenterol76: 978-982.
Fayol V, Hassanein HI, El-Badrawy N, Ville G, Hartmann DJ 1991. Aminoterminal propeptide of type III procollagen: a marker of disease activity in schistosomal patients. Eur J Clin Chem Clin Biochem9: 737-741.
Hirata M, Kage M, Takushima M, Fukuma T 1993. Different courses of granulomatous reactions around S. japonicum eggs in three strains of mice. J Parasitol79: 266-273.
Hood AT, Boros DL 1980. The effect of splenectomy on the pathophysiology and egg-specific immune response of Schistosoma mansoni-infected mice. Am J Trop Med Hyg29: 586-591.
Mincis M, Braga LLC, Russo EMK, Novo NF, Juliano Y 1990. Serum type III procollagen peptides in patients with hepatointestinal and compensated hepatoesplenic schistosomiasis forms. Arq Gastroenterol São Paulo27: 24-29.
Monteiro A, Borojevic R 1995. Complement-dependent induction of DNA-synthesis and cell-proliferation in human liver connective-tissue cells in-vitro. In Vitro Cellular Dev Biol-Animal31: 149-155.
Montesano MA, Freeman GL, Gazzinelli G, Colley DG 1990. Immune responses during human Schistosoma mansoni. XVII. Recognition by monoclonal anti-idiotypic antibodies of several idiotypes on a monoclonal anti-soluble schistosomal egg antigen antibody and anti-soluble schistosomal egg antigen antibodies from patients with different clinical forms of infection. J Immunol145: 3095-3099.
Olds GR, Kresina TF 1989. Immunoregulation of hepatic fibrosis in murine schistosomiasis japonica. J Infect Dis159: 798-801.
Olds GR, Meneza S el, Mahmoud AAF, Kresina TF 1989. Differential immunoregulation of granulomatous inflammation, portal hypertension, and hepatic fibrosis in murine schistosomiasis mansoni. J Immunol142: 3605-3611.
Parise ER, Rosa H 1992. Serum laminin in hepatic schistosomiasis. Trans R Soc Trop Med Hyg86: 179-181.
Parra JC, Gazzinelli G, Goes AM, Moyes RB, Rocha R, Colley DG, Doughty BL 1991. Granulomatous hypersensitivity to Schistosoma mansoni egg antigens in human schistosomiasis. II. In vitro granuloma modulation induced by polyclonal idiotypic antibodies. J Immunol147: 3949-3954.
Postlewaite AE, Holness MA, Kitai H, Raghow R 1992. Human fibroblasts synthesize elevated levels of extracellular matrix proteins in response to interleukin 4. J Clin Invest90: 1479-1485.
Shahin M, Schuppan D, Waldherr R, Risteli J, Tisteli L, Savolainen E-R, Oesterling C, Abdel Rahman HM, El Sahly AM, Abdel Razek SM, El Ruby O, Koch A, Seitz HK 1992. Serum procollagen peptides and collagen type VI for the assessment of activity and degree of hepatic fibrosis in schistosomiasis and alcoholic liver disease. Hepatology15: 637-644.
Shahin M, Schuppan D, Waldherr R, Zalpur F, Rahman HM, Elsahly AM, Razek SMA, Elruby O, Seitz HK 1995. Hepato-Gastroenterology42: 22-26.
Tanabe M, Sekiguchi T, Kaneko N, Kobayashi S, Takeuchi T, Coutinho A, Tateno S, Maruyama K, Okazaki I 1989. Elevation of laminin and beta-subunit prolyl 4-hydroxylase in the sera of human subjects with Schistosoma mansoni. Japan J Exp Med39: 109-119.
Weinstock JV, Ehrinpreis MN, Boros DL, Gee JB 1981. Effect of SQ 14225, an inhibitor of angiotensin I-converting enzyme, on the granulomatous response to Schistosoma mansoni eggs in mice. J Clin Invest67: 931-936.
Wynn TA, Cheever AW, Jankovic, D, Poindexter RW, Caspar P, Lewis FA, Sher A 1995. An Il-12 based vaccination method for preventing fibrosis induced by schistosome infection. Nature376: 594-596.
Zwingenberger KG, Harms H, Feldmeier O, Muller A, Steiner A, Bienzle U 1988. Liver involvement in human schistosomiasis mansoni. Regression of immunological and biochemical disease markers after specific treatment. Acta Tropica45: 263-275.