Defects in mononuclear phagocytic system (MPS) function in autoimmune MRL-lpr/lpr mice

Dysregulated cytokine expression in vivo in prediseased and diseased autoimmune-prone MRL mice

Macrophages (mø) from prediseased autoimmune-prone MRL/ + and MRL/lpr mice produce markedly decreased levels of IL-1 in vitro in response to LPS. In contrast, tissues from diseased MRL/lpr mice overexpress IL-1 in vivo. To determine whether IL-1 underproduction in the MRL strains is solely an in vitro phenomenon, we compared in vivo cytokine mRNA expression from prediseased age-matched MRL/ + and MRL/lpr mice to that from normal BALB/c and C3HeB/FeJ mice. Like mø in vitro, whole organ RNA from the spleen, liver, and kidney of MRL/ + and MRL/lpr mice showed down-regulation of IL-1 RNA following intraperitoneal injection of LPS. This abnormality in inducible IL-1 expression was present in all MRL mice, irrespective of disease stage or the presence of the lpr gene. On the other hand, only diseased MRL/lpr mice displayed elevated and constitutive expression of IL-1 in their livers and kidneys. We suggest that inducible expression is most indicative of the intrinsic, or genetic, capacity of cells to produce cytokine, whereas constitutive expression reflects extracellular disease-related inflammatory stimuli present only in the diseased MRL/lpr strains. By restricting our studies to prediseased MRL mice, we have tried to eliminate the effects of disease and to focus on the predisposing genetic background. The existence both in vitro and in vivo of a defect in inducible IL-1 expression by prediseased MRL mice suggests that the molecular abnormality underlying this defect may be a part of this predisposing background to autoimmunity.

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.

Spontaneous development of pancreatitis in the MRL/Mp strain of mice in autoimmune mechanism

MRL/Mp mice are known to have autoimmune disease-prone genetic background, which contributes to the development of a lethal autoimmune disease at an early age in association with the lymphoproliferative gene, lpr. In this study, we found that MRL/Mp mice, not bearing lpr (MRL/Mp-(+)/+), spontaneously developed pancreatitis at a late stage of life, which was histopathologically characterized by destruction of pancreatic acinar cells with mononuclear cell infiltration. In female 34-38-weeks-old mice the incidence of pancreatitis reached 74%, whereas the male mice developed the disease with a reduced incidence, at a later stage of life and with a reduced severity. Cell infiltrates in the affected lesions were composed predominantly of CD4+ cells and to lesser extent Mac-2+ macrophages. Adoptive transfer of the spleen cells obtained from pancreatitis-bearing female mice generated pancreatitis in female normal mice, but not in the male mice. Transfer of the serum of pancreatitis-bearing mice failed to induce any pancreatic lesions. These findings indicate that pancreatitis in MRL/Mp-(+)/+ mice may be mediated by cellular autoimmune mechanism. This may present a useful concept for analysis of the developmental mechanisms of human chronic pancreatitis in an aspect of autoimmunity.

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

5'-Nucleotidase (5'N) activity and Ia expression of hepatic nonparenchymal cells (NPCs) of the autoimmune (NZB X NZW)F1 and MRL-lpr/lpr and nonautoimmune C3H/FeJ, DBA/2J, and A/J strains were assayed to determine endogenous activation of the hepatic reticuloendothelial system (RES). Pretreatment of the nonautoimmune strains with Corynebacterium parvum resulted in decreases in Fc receptor expressor and 5'N and an increase in Ia expression of NPCs. Endogenous hepatic RES activation, as measured by low 5'N and high Ia expression, was observed in both the autoimmune MRL-lpr/lpr and (NZB X NZW)F1 strains even without C. parvum pretreatment. However, in the MRL-lpr/lpr strain, age is a dependent variable in activation and correlates with delayed clearance from the circulation of soluble IgG immune complexes. In the (NZB X NZW)F1 strain, the observation of decreased 5'-nucleotidase activity and increased percentage of Ia-positive cells at all ages suggests a primary abnormality. Therefore, different genetic or exogenous factors may be responsible for the activation of the hepatic RES in these autoimmune strains.