Hepatic reticuloendothelial system activation in autoimmune mice: differences between (NZB X NZW)F1 and MRL-lpr/lpr strains

Rodent preclinical models for developing novel antiarthritic molecules: comparative biology and preferred methods for evaluating efficacy

Rodent models of immune-mediated arthritis (RMIA) are the conventional approach to evaluating mechanisms of inflammatory joint disease and the comparative efficacy of antiarthritic agents. Rat adjuvant-induced (AIA), collagen-induced (CIA), and streptococcal cell wall-induced (SCW) arthritides are preferred models of the joint pathology that occurs in human rheumatoid arthritis (RA). Lesions of AIA are most severe and consistent; structural and immunological changes of CIA best resemble RA. Lesion extent and severity in RMIA depends on experimental methodology (inciting agent, adjuvant, etc.) and individual physiologic parameters (age, genetics, hormonal status, etc.). The effectiveness of antiarthritic molecules varies with the agent, therapeutic regimen, and choice of RMIA. All RMIA are driven by overactivity of proinflammatory pathways, but the dominant molecules differ among the models. Hence, as with the human clinical experience, the efficacy of various antiarthritic molecules differs among RMIA, especially when the agent is a specific cytokine inhibitor.

Fc receptors in liver sinusoidal endothelial cells in NZB/W F1 lupus mice: a histological analysis using soluble immunoglobulin G-immune complexes and a monoclonal antibody (2.4G2)

In systemic lupus erythematosus accompanied by the abnormal appearance of circulating immune complexes (ICs), Fc gamma receptor (FcR)-mediated IC handling in macrophages including Kupffer cells has been shown previously. However, sinusoidal endothelial cells (SECs) largely ingest soluble immunoglobulin (Ig) G-ICs through FcRs. In this study, the character, antigenic expression, and activity (i.e., ligand-binding capacity of SEC FcRs in NZB/NZW F1 lupus and NZW nonautoimmune mice) were immunohistochemically analyzed using monoclonal antibody (MAb) 2.4G2 to FcRs and peroxidase-antiperoxidase IgG as a ligand on cryosections. MAb 2.4G2 stained SECs and blocked the ligand binding of SEC FcRs in both mice strains. The staining intensities with MAb 2.4G2 in SECs and the FcR activities in SECs alone and all sinusoidal cells in both mice strains reached their maximum values at the age of 5 months. Staining intensities in NZB/W F1 were significantly higher at 1 and 2 months and lower at 9 months than those in NZW. The number of Kupffer cells detected by MAb F4/80 to macrophages in both mice strains gradually increased until 5 months, but their number in NZB/W F1 at 9 months was twice as large as that in NZW. In conclusion, SEC FcRs in mice are low-affinity FcRs that react with MAb 2.4G2. The data of FcR activity suggest no impairment of the FcR-mediated IgG-IC binding on SECs in NZB/W F1 in early life.(ABSTRACT TRUNCATED AT 250 WORDS)

Immune complex-degradation ability of macrophages in MRL/Mp-lpr/lpr lupus mice and its regulation by cytokines

Impaired clearance of circulating and/or deposited immune complexes (IC) by the mononuclear phagocytic system is one of the major factors in the pathogenesis of IC diseases. MRL/Mp-lpr/lpr (MRL/lpr) lupus mice spontaneously develop a lethal glomerulonephritis associated with IC deposition. The ability of macrophages to degrade phagocytozed IC and regulation of this degradation in MRL/lpr mice were examined. In 4-month-old MRL/lpr mice, macrophages accumulated in the affected glomeruli and these macrophages contained many phagosomes containing electron-dense bodies. When culture supernatant of human T cell line HUT102 was administered intraperitoneally into disease-bearing MRL/lpr mice, degradation of these electron-dense bodies in the macrophages in glomeruli was noted. We developed a quantitative in vitro assay for IC degradation activity of MRL/lpr resident peritoneal macrophages (RPM) using peroxidase-labelled IC derived from MRL/lpr mouse sera. The ability of the RPM to degrade IC was remarkably enhanced by the pretreatment with HUT102 cell products and the related human recombinant cytokines, lymphotoxin and IL-1 alpha. Moreover, pretreatment of RPM from non-diseased MRL/Mp-+/+ mice with the culture supernatant of spleen cells from diseased MRL/lpr mice reduced their IC degradation activity. These results suggested that the ability of macrophages to degrade IC in MRL/Mp strains of mice is under the regulation of cytokines, and the impaired ability in the disease-bearing mice may be the result of abnormalities in the cytokine system in these mice.

Interleukin-1 dysregulation is an intrinsic defect in macrophages from MRL autoimmune-prone mice

Macrophages (M phi) from pre-diseased autoimmune-prone MRL mice (both MRL/+ and MRL/lpr) dramatically underproduce the cytokine interleukin-1 (IL-1) in comparison to M phi from a number of normal strains. In this study we show that IL-1 dysregulation by MRL M phi is fully expressed at birth, and that this defect does not change with time or the development of disease. We also constructed adult irradiation chimeras (consisting of A/J-->MRL and MRL-->A/J mice), and show that M phi isolated from these chimeras display a pattern of IL-1 production indistinguishable from that of the donor strain controls. Moreover, when we constructed a mixed chimera (A/J + MRL-->A/J, the A/J and MRL M phi coexisting within the same animal retained their individual patterns of IL-1 production when isolated by negative selection. Taken together, these results provide the first substantive evidence for an intrinsic defect (IL-1 dysregulation) in M phi from MRL autoimmune-prone mice.

Modulation of murine hepatic lipase activity by exogenous and endogenous Kupffer-cell activation

Deficiency of hepatic lipase (HL) may play a role in the lipoprotein abnormalities in chronic inflammatory states which are characterized by reticuloendothelial-system activation and cytokine release. HL triacylglycerol hydrolase activity was measured in heparin perfusates of livers from autoimmune MRL/lpr mice, which spontaneously develop a condition closely resembling human lupus erythematosis and exhibit spontaneous Kupffer-cell activation after 8 weeks of age, as well as from normal mice treated with Corynebacterium parvum or polyinosinic-polycytidylic acid complex [poly(I.C)] to induce Kupffer-cell activation. HL activity in MRL/lpr mice older than 8 weeks was 29.5% (P = 0.002) of that in age-matched control MRL/++ mice. Treatment of normal mice with C. parvum or poly(I.C) resulted in HL activities 18.6% (P = 0.004) and 13.1% (P = 0.007) respectively of untreated controls. Northern-blot hybridization of liver poly(A)+ RNA showed no differences in HL mRNA abundance in MRL/++ mice compared with the MRL/lpr autoimmune strain after 8 weeks of age, or in normal control mice compared with those treated with C. parvum, indicating attenuation of HL activity at the translational or post-translational level. Deficiency of this enzyme may represent one of the mechanisms contributing to the dyslipoproteinaemia of autoimmune disease and chronic infection.

Liver of MRL/lpr mice contain interleukin-4-producing lymphocytes and accessory cells that support the proliferation of Th2 helper T lymphocyte clones

Hepatic nonparenchymal cells (NPC) from mice of nonautoimmune strains support the proliferation of only Th1 and not Th2 helper T lymphocyte (HTL) clones. Because of the multiple systemic and liver-specific immune defects in the autoimmune MRL/lpr mouse strain, we have explored the possibility that hepatic accessory cells from MRL/lpr mice are capable of stimulating the proliferation of Th2 HTL. We report here that hepatic NPC from MRL/lpr and C3H/lpr female mice older than 8 weeks, in contrast to hepatic NPC from MRL/++ and C3H/HeN strains, are able to support in vitro the proliferation of both Th1 and Th2 CD4 clones. Additionally, hepatic lymphocytes (HL) from MRL/lpr mice can be stimulated to produce interleukin (IL)-4 to a much higher degree than HL from the nonautoimmune strains. These results suggest that the activation of Th2 cells by hepatic NPC and production of IL-4 by HL may contribute to the immunologic aberrations in the MRL/lpr mouse strain.

Expansion and high proliferative potential of the macrophage system throughout life time of lupus-prone NZB/W and MRL lpr/lpr mice. Lack of down-regulation of extramedullar macrophage proliferation in the postnatal period

Systemic lupus erythematosus is an autoimmune disease, characterized by high titers of autoantibodies against many cell-membrane and intracellular antigens. Polyclonal B cell activation and alterations in the T cell compartment have been described. The present report deals with the organ-associated macrophage (M phi) system of two lupus-prone mouse strains (NZB/W and MRL lpr/lpr) and demonstrates that in both mouse strains the M phi compartment of liver and spleen is clearly expanded. In the liver the number of F 4/80+ M phi is strongly elevated. In addition, presence of early M phi precursors and of extramedullary organ-associated monocyte proliferation in response to colony-stimulating factor (CSF) is documented in liver and spleen of these mice. Further, in normal animals during the first two weeks of life extramedullar monocytopoiesis is present in liver and spleen, which is then down-regulated in the third week of life. In the two lupus-prone mouse strains down-regulation does not occur but extramedullar monocyte proliferation is sustained at high level throughout life time. As possible correlates for the expansion of the M phi system elevated CSF-1 mRNA levels are demonstrated in kidney, spleen and liver of NZB/W mice and elevated CSF serum levels are documented in MRL lpr/lpr mice. The possible contribution of the expanded M phi system to B and T cell dysregulation is discussed.

The liver of MRL/lpr mice contains defective accessory cells and a population of immunosuppressive lymphocytes

Immunoregulatory abnormalities in the MRL/lpr mouse strain include activation of macrophages and hepatic natural killer cells, spontaneous production of tumor necrosis factor, defective oral tolerance, and impaired production of interleukin-2. Because the liver is the major organ responsible for the clearance, degradation, and presentation of foreign antigens from the gastrointestinal tract, we have investigated antigen presentation activity of hepatic nonparenchymal cells (NPC) from MRL/lpr, MRL/++, and C3H/HeN female mice in the primary immune response as measured by stimulation of allogeneic one-way mixed lymphocyte response (MLR), and allogeneic cell-mediated lympholysis (CML). Whereas adherent NPC from C3H/HeN, MRL/++, and young MRL/lpr mice were effective stimulators, NPC from MRL/lpr mice older than 9 weeks were defective stimulators of both MLR and CML responses. This abnormality was not observed in splenic accessory cells from these mice. Moreover, a population of hepatic NPC from older MRL/lpr mice are immunosuppressive: mixing of MRL/lpr NPC with splenic stimulators from MRL/++ mice profoundly inhibited primary allogeneic CML responses. The inhibitory hepatic nonparenchymal cell population was nonadherent, radioresistant and was removed by pretreatment with antibodies to either asialoAGM-1 or Lyt-2 plus complement. This inhibition was not observed with the addition of MRL/++ NPC or supernates from cultured MRL/lpr NPC. These findings suggest a selective organ-specific and age-dependent impairment of antigen presentation and the presence of an immunosuppressive lymphocyte population in the liver of MRL/lpr mice which may contribute to the autoimmune process.

Alterations in Fc receptor activity in sinusoidal endothelial cells and Kupffer cells during D-galactosamine (GalN)-induced liver injury in rats. A histological study

Fc receptors in sinusoidal cells and immune complex uptake were studied histologically in D-galactosamine HCl (GalN)-induced liver injury in rats. Kupffer cells and monocytes were distinguished from sinusoidal endothelial cells and from each other by endogenous peroxidase staining. Fc receptors were found along the sinusoidal endothelium throughout the lobules in normal livers. In acute injury caused by 300 or 750 mg/kg of GalN, Fc receptors were preserved within necrotic foci until the foci were infiltrated by inflammatory cells. The endothelial Fc receptor activity altered, as demonstrated by their capacity to bind immune complexes, after GalN injection. The activity decreased from 24 h after injection in the periportal areas in both dose groups, and increased transiently with dose-dependence in the remaining areas. Kupffer cell numbers also showed a transient dose-dependent increase, except in the periphery of lobules where they generally decreased. In chronic injury with 400 mg/kg, Fc receptors were lost and Kupffer cells decreased in the periportal areas. Circulating immune complexes were ingested by Kupffer cells and endothelial cells in normal and injured livers, showing the the same distribution as that of Fc receptors except that the complexes decreased gradually towards the centrilobular zones.

A comparison of murine hepatic accessory cells and splenic dendritic cells

Accessory cells are required for proliferation and antibody synthesis of B lymphocytes and proliferation of T lymphocytes in primary immune responses in vitro. The obligatory cells derived from the spleen are referred to as dendritic cells. Accessory cells were isolated from normal adult livers which were functionally interchangeable with splenic DC. Both hepatic accessory cells (AC) and splenic DC adhere firmly to plastic culture dishes or wells within 2 hr; but hepatic AC, unlike splenic DC, do not detach during 22 hr additional incubation. Hepatic AC, unlike splenic DC, are not lysed or inactivated by monoclonal antibody 33D1 and C'. Hepatic AC and splenic DC are similarly sensitive to irradiation in vivo and insensitive to irradiation in vitro. Hepatic AC are separated with cells which are predominantly phagocytic and FcR+ and contain nonspecific esterase. Both hepatic AC and splenic DC are suppressed or eliminated by activation of NK cells in vivo, a phenomenon prevented by prior elimination of NK cells.

Spontaneous production of tumor necrosis factor alpha by Kupffer cells of MRL/lpr mice

We report that freshly isolated, unstimulated Kupffer cells (KC) from MRL/lpr female mice in short-term culture spontaneously produce high levels of TNF-alpha. TNF production was first detected in KC cultures at age 6 wk and increased with the age of the mice. Moreover, the levels of spontaneous TNF production by KC directly correlated with the age of the MRL/lpr mice. Although TNF production by KC could be induced with C. parvum in vivo or LPS in vitro in all nonautoimmune C3H/HeN, BALB/c, DBA/2, C57B16 mice, the only other strain in which spontaneous TNF production by KC was observed was MRL/++ mice greater than 10 mo old.

High hepatic natural killer cell activity in murine lupus

This study demonstrates a profound elevation of NK activity, as measured by cytotoxicity to YAC-1 targets in a 4-h incubation 51Cr-release assay, of freshly isolated hepatic NPC from both MRL/lpr and (NZB X NZW)F1 mice. This marked increase was not observed in splenic or peripheral blood NK. The hepatic NK were nonadherent, radioresistant, Ly-1-,2-, and AGM1+. Furthermore, biologic response modifiers can further augment hepatic NK activity in these autoimmune strains.