Relationship between interleukin 6, agalactosyl IgG and pristane-induced arthritis.

IL-6 titres in sera and peritoneal exudate fluids (PEF) derived from pristane injected DBA/1 and CBA/Igb mice were measured. Arthritic DBA/1 mice had significantly higher serum IL-6 titres than nonarthritic or normal mice at 160 days post pristane injection. By contrast, although both arthritic and non-arthritic CBA/Igb mice had higher serum IL-6 titres than normal mice, there was no significant difference in serum IL-6 titre between these two groups at day 200-230. In both strains of mice, the IL-6 titres in PEF were more than 10 times serum levels regardless of arthritis. As previously reported for CBA/Igb mice, agalactosyl IgG levels are raised in pristane injected DBA/1 mice and the percentage is higher in arthritic animals than that in non-arthritic mice. An association between serum agalactosyl IgG levels and PEF IL-6 in pristane injected DBA/1 was demonstrated. Moreover, the injection of recombinant IL-6 into normal mice increased their serum agalactosyl IgG levels. However, it is considered that IL-6 is not the only factor involved in the production of agalactosyl IgG.     

The role of IgG glycoforms in the pathogenesis of rheumatoid arthritis

Conclusions In conclusion, there is a shift in the population of IgG glycoforms towards those with a higher content of agalactosyl biantennary N-linked oligosaccharides in active rheumatoid arthritis (both juvenile and adult), tuberculosis, and Crohn's disease, but not in a variety of other rheumatological, inflammatory, or infectious conditions. This shift may contribute to disease pathogenesis both through immune-complex formation and through disturbance of a cellular network directed against the non-reducing terminal G1cNAc epitope. The precise pathology would in each case be modulated by the anatomical site(s) of production of such IgG, and also by the precise mechanism inducing this change in IgG glycosylation. Important amongst such mechanisms may be cross-reactivity between environmental and endogenous carbohydrate epitopes. It will be interesting to see if future research supports the idea that groups of diseases (e. g., rheumatoid arthritis, tuberculosis, Crohn's) are indeed related by a common aetiopathogenesis [i. e., G(0)].     

An analysis of piroxicam in rodent models of arthritis

Piroxicam, a potent, long acting non-steroidal anti-inflammatory drug, was tested in several rodent models of arthritis to assess further the possible mechanisms underlying its anti-inflammatory action. Piroxicam inhibited rat adjuvant disease and its associated manifestations, which include erosion of bone and cartilage (as evidenced by X-ray examination), soft tissue swelling and disease-induced weight loss. Piroxicam also inhibited the edema, the total leukocyte infiltration and the mononuclear cell infiltration into the carrageenan-injected pleural cavity of the rat. The possible relationship of these effects to the clinical activity of piroxicam is discussed.     

On the interaction between agalactosyl IgG and Fcγ receptors

One of the serum abnormalities observed in autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is the occurrence of IgG that lacks the terminal galactose on asparagine-linked biantennary complex type oligosaccharides [Gal(0)-IgG] located in the CH2 domain. Additionally, IgG without glycosylation is known to be defective in several effector functions due to a reduced ability to bind to its specific receptors (FcγR). It has thus been speculated that, by analogy with unglycosylated IgG, Gal(0)-IgG may also be functionally impaired or exert altered effector mechanisms. If this were true, Gal(0)-IgG could contribute to the phenotype of above-mentioned autoimmune diseases, like impaired immune complex clearance and defective down-regulation of activated B cells. Here, we show by three different methods that the interaction of Gal(0)-IgG and normally glycosylated IgG with the low-affinity FcγRII (CD32) is indistinguishable with respect both to binding and receptor-mediated signalling. These data argue against a prominent role for FcγR-dependent Gal(0)-IgG interactions in the etiology or pathogenesis of autoimmune diseases.     

Comparison between the protective effects of mycobacterial 65-kD heat shock protein and ovomucoid in pristane-induced arthritis: relationship with agalactosyl IgG.

The IgG of patients with rheumatoid arthritis and mice with pristane induced arthritis (PIA) tends to lack the terminal galactose normally on the conserved N-acetylglucosamine linked beta 1-2 to mannose in IgG. The terminal N-acetylglucosamine (GlcNAc) residues of oligosaccharides on agalactosyl IgG may be an important component of the action of these glycoforms. Here, administration of ovomucoid, a glycoprotein rich in terminal GlcNAc, before pristane injection was found to reduce the incidence of PIA. This observation is the second report of an intraperitoneally administered antigen that reduces the incidence of PIA, mycobacterial 65-kD heat shock protein (hsp65) being the first. The suppressive effect of ovomucoid was not transferred from protected to naive recipients by spleen cells at the dose tested. By contrast, transfer of spleen cells from hsp65-protected mice to naive recipients conferred protection and this protection may be antibody-mediated. It is considered that ovomucoid and hsp65 protect against the development of PIA by different mechanisms.     

Contribution of genetic studies in rodent models of autoimmune arthritis to understanding and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic and potentially debilitating autoimmune disease. While novel therapies have emerged in recent years, disease remission is rarely achieved. RA is a complex trait, and the identifying of its susceptibility and severity genes has been anticipated to generate new targets for therapeutic intervention. However, finding those genes and understanding their function has been a challenging task. Studies in rodent intercrosses and congenics generated from inbred strains have been an important complementary strategy to identify arthritis genes, and understand how they operate to regulate disease. Furthermore, these new rodent arthritis genes will be new targets for therapeutic interventions, and will identify new candidate genes or candidate pathways for association studies in RA. In this review-opinion article I discuss RA genetics, difficulties involved in gene identification, and how rodent models can facilitate (1) the discovery of both arthritis susceptibility and severity genes, (2) studies of gene-environment interactions, (3) studies of gene-gender interactions, (4) epistasis, (5) functional characterization of the specific genes, (6) development of novel therapies and (7) how the information generated from rodent studies will be useful to understanding and potentially treating RA.     

Possible role of microbial IgG Fc-binding proteins in rheumatoid arthritis

IgG Fc binding substances (receptors) are widespread among pathogenic microorganisms. The receptors fromStaphylococcus aureus, streptococci of group A, C and G as well asHerpes-infected cells bind to the interface between the CH2 and CH3 domains i.e. to His 435, Tyr 436 and possibly also His 433 and/or 310. Most rheumatoid factors (RF) from patients with rheumatoid arthritis show a similar binding pattern. Hence, it has been shown that antibodies to microbial IgG Fc receptors (S. aureus and group A streptococci type M15) and RF are idiotypic — anti-idiotypic antibody partners i.e. that RF are the internal images of microbial IgG Fc binding proteins. Group A streptococci possessing IgG Fc receptors elicit higher titres of RF when injected in rabbits as compared to group A streptococci without IgG Fc receptors. The streptococcal IgG Fc receptors exhibit a diversity of preferences for subclasses of human IgG, some of them showing allotype preferences. Such allotypes are also recognized by certain RF. IgG RF are able to self-associate thereby forming immune complexes which can activate the complement cascade as well as stimulate release of prostaglandins and (probably) interleukin-1. Since these factors have been assigned an important pathogenic role in rheumatoid arthritis, self-aggregating IgG RF, proposed to be induced by microbial IgG Fc receptors might be an important pathogenic factor in rheumatoid arthritis because rheumatoid arthritis is the only known condition where synthesis of RF takes place in the synovia.     

IgM plays an important role in induction of collagen-induced arthritis

IgM is one major type of B cell receptor (BCR) expressed on most of the B cells from immature to mature stages. During normal B cell ontogeny, signals transduced through the IgM BCR play an important role in regulating B cell maturation and survival at multiple checkpoints. In addition, IgM BCR is also required for antigen-dependent differentiation and activation of B cells. However, whether IgM BCR-mediated signalling is important for the pathogenesis of autoimmune diseases remains elusive. Using IgM-deficient mice, we examined the effect of absence of IgM on the development of collagen-induced arthritis (CIA), an animal model of rheumatoid arthritis (RA). Compared to their wild-type littermates, IgM-deficient mice were either resistant to arthritis induction or developed significantly less severe arthritis. There was a significant decrease of autoantibody production in IgM-deficient mice, particularly IgG2a antibodies, which is believed to be pathogenic in CIA. Thus, although IgM(-/-) mice have relatively normal B cell development with IgD BCR replacing IgM BCR, the absence of IgM-mediated signals has a profound impact on the development of CIA, indicating that IgM plays an important role in the development and pathogenesis of autoimmune arthritis and IgM-mediated signalling is critical in the generation of pathogenic autoreactive antibodies.     

Agalactosyl IgG in pristane-induced arthritis. Pregnancy affects the incidence and severity of arthritis and the glycosylation status of IgG.

The effect of pregnancy on the incidence and severity of pristane-induced arthritis was examined along with the glycosylation status of IgG during the ante-natal and post-partum periods. It was found that pristane-induced arthritis is prevented by pregnancy. In addition, the levels of agalactosyl IgG fall during pregnancy but rise to greater than normal within a few days of parturition, before resetting towards the norm shortly afterwards. Interestingly, the level of agalactosyl IgG correlates with the severity of arthritis. As previously reported IL-6 may be an important factor, not necessarily the only one, in the production of agalactosyl IgG. Here it is clearly demonstrated that the kinetics of IL-6 activity post-pristane injection parallels the kinetics of agalactosyl IgG production. In addition, the overshoot in agalactosyl IgG levels immediately post-partum coincides with a burst in IL-6 activity. It is considered that these changes in IgG glycoform levels, or the factors which control them, may be related to the mechanisms underlying prevention/remission of arthritis during pregnancy.     

The measurement of IgG anti-IgG antibody in rheumatoid arthritis

Serum IgG anti-IgG antibody was measured in patients with rheumatoid arthritis and osteo-arthritis and in healthy young adults. The antibody was isolated by immunoadsorption and evaluated by titration with latex particles. After establishing the method's specificity for IgG anti-IgG, its reproducibility and a means for converting titer to IgG concentration, IgG anti-IgG was found in greatest amounts in rheumatoid arthritis when compared with two other groups. The concentration of IgG anti-IgG, however, was consistently lower in our study than in studies by other workers. This discrepancy appears to be related to our procedure, namely dilution of serum prior to exposure to immunoadsorption, the latter tending to dissociate immune complexes (removal of IgG antigen from IgG anti-IgG antibody). The eluate obtained in this manner contains antibody IgG freed of IgG antigen, as manifested by mainly 7 S IgG, rather than 7 S IgG admixed with complexes of higher sedimentation coefficients. The method reported in this article, therefore, appears to measure IgG anti-IgG antibody with a greater degree of accuracy than previously reported techniques.     

A longitudinal study of per cent agalactosyl IgG in tuberculosis patients receiving chemotherapy, with or without immunotherapy.

An increased percentage of circulating IgG molecules that lack galactose from the oligosaccharides on the CH2 domain correlates with disease severity in tuberculosis, rheumatoid arthritis and Crohn's disease. We have recently observed that a single injection of 10(9) autoclaved Mycobacterium vaccae given to tuberculosis patients 7 days after the initiation of chemotherapy causes accelerated clinical improvement, and clearance of bacilli from the sputum. We now show that this immunotherapy also causes rapid loss of agalactosyl IgG, detectable within 14-21 days, whereas chemotherapy alone causes agalactosyl IgG to rise further for up to 2 months. There is simultaneous inhibition of the antibody response to lipoarabinomannan, and transient enhancement of the tuberculin skin-test response. These findings are compatible with a shift from antibody production towards increased cell-mediated immunity. The ideal treatment for tuberculosis would supplement a truncated course of chemotherapy with an immunotherapeutic preparation able to down-regulate the Koch phenomenon and replace it with an efficiently bactericidal mechanism. We tentatively postulate that a fall in per cent agalactosyl IgG [%Gal(0)] in tuberculosis patients may be a marker of such a change.     

Abnormal IgG galactosylation in MRL-lpr/lpr mice: pathogenic role in the development of arthritis

MRL-lpr/lpr (MRL/lpr) mice spontaneously develop arthritis by an increase in the incidence of agalactosylated oligosaccharides in serum IgG, similar to rheumatoid arthritis patients. However, whether this association has a pathogenic significance is still unknown. In this study, we analyzed the oligosaccharide structure of serum IgG in various MRL mice with or without arthritis, to clarify the relationship between the oligosaccharide abnormality and the development of arthritis. The level of agalactosylation in serum IgG was comparable in both arthritis-free MRL/lpr and MRL-+/+ (MRL/+) mice at 6 weeks of age. In contrast, the incidence of IgG lacking galactose markedly increased in MRL/lpr mice at 6 months of age (the age at which arthritis occurred), compared with that from age-matched MRL/+ mice without arthritis. However, the proportion of agalactosylated IgG increased similarly in anti-CD4 monoclonal antibody-treated MRL/lpr mice at 6 months of age, despite the absence of the development of arthritis, because of depletion of CD4+ T cells. These results suggest that the abnormality in IgG galactosylation of MRL/lpr mice developed in an age-dependent manner, but it did so independently of CD4+ T cell-dependent B-cell activation and is not a consequence of the development of arthritis.     

An immunofluorescence study of IgG receptors in rodent enterocytes

Locations of IgG receptors in the small intestine of suckling rats were visualized by treating sections of the gut with IgG and FITC-labelled anti-IgG antibodies. Receptors, operative optimally at acid pH, occurred only in younger rats whose intestines were still permeable to antibodies; they were located on the brush borders of the enterocytes on the apical parts of the villi in the duodenum and jejunum. Premature disappearance of the receptors from the gut was achieved by cortisone treatment. In rats and mice, IgG from different species each competed for attachment to the receptors in vitro in the same way as it inhibited the transmission of other IgG across the intestine in vivo, thus reflecting the involvement of the receptors in the transport mechanism.     

IgG subclasses in collagen-induced arthritis in the rat

Mitogenic lymphocyte stimulation with six concentrations of phytohemagglutinin (PHA) was compared in 60 patients with advanced or metastatic cancer and 30 age- and sex-matched healthy controls using an optimized whole blood method. Since the method is simple and the number of technical variables relatively small, a "normal" range of PHA responsiveness expressed in absolute cpm, could be established. It is thus possible to directly compare results from different laboratories. A markedly reduced lymphocyte stimulation was found in cancer patients compared to controls, although leukocyte and lymphocyte counts were almost "normal". The implications of this finding are discussed with regard to immunosuppression by the tumor and previous chemotherapy.     

Biological roles of rodent anaphylactic IgG1 antibodies

Described and mainly studied in guinea-pigs and mice (Benacerraf, Ovary, Bloch and Franklin, 1963; Fahey, Wunderlich and Mishell, 1964) (but also demonstrated in rats and hamsters, and others), IgG₁ immunoglobulins are a fascinating class of antibodies. Long known for their anaphylactic properties, they have now been also studied in our laboratory for their cooperative, protective and immunoregulatory properties. Like other immunoglobulin classes of antibody, their biological activity is exerted through their Fc portion and expressed only after the immunoglobulin has been activated by fixation on corresponding antigen through their Fab portions.My purpose is to present a summary of the work done in our laboratory on the biological role of IgG₁ antibodies.This presentation will be divided into 3 parts respectively concerned with their inflammatory properties in specific hypersensitivity reactions such as anaphylaxis and Arthus, their protective action (as a final result) of the antigenbearing target in the facilitation reaction, and finally the relations (and common denominator) between the two types of properties.     

The role of IgG4 in cutaneous pathology

IgG4 is an immunoglobulin subtype that has many physiologic and morphologic peculiarities. In cutaneous pathology, IgG4 has been related to the pathogenesis of many diseases. Moreover, in the recent years, new IgG4-related diseases have been described. Since some involve the skin, either primarily or as part of their systemic manifestations, we have tried to briefly examine some of the cutaneous conditions related to IgG4.     

Anti-epileptogenesis in rodent post-traumatic epilepsy models

Post-traumatic epilepsy (PTE) accounts for 10-20% of symptomatic epilepsies. The urgency to understand the process of post-traumatic epileptogenesis and search for antiepileptogenic treatments is emphasized by a recent increase in traumatic brain injury (TBI) related to military combat or accidents in the aging population. Recent developments in modeling of PTE in rodents have provided tools for identification of novel drug targets for antiepileptogenesis and biomarkers for predicting the risk of epileptogenesis and treatment efficacy after TBI. Here we review the available data on endophenotypes of humans and rodents with TBI associated with epilepsy. Also, current understanding of the mechanisms and biomarkers for PTE as well as factors associated with preclinical study designs are discussed. Finally, we summarize the attempts to prevent PTE in experimental models.     

The role of carbohydrate in the assembly and function of polymeric IgG

The carbohydrate present on glycoprotein can influence their biologic and functional properties. In the present paper we have assessed the role of oligosaccharides in the polymerization and effector functions of IgG with the 18 amino acid extension of IgM added to its carboxy terminus (IgGμtp). We found that IgG1μtp and IgG3μtp lacking the carbohydrate addition site in C_H2, in the tail-piece or both assembled into polymers as well as the glycosylated versions. Aglycosylated polymers retained the ability to activate complement as assayed by C1q binding and hemolysis, although they were not as effective as their wild type polymer counterparts. Although IgGμtp lacking the carbohydrate in the tail-piece was able to bind to FcγRII, completely aglycosylated polymers lost the ability to bind to both FcγRI and FcγRII, suggesting a critical role for the C_H2 sugar in FcR binding. Absence of the μtp carbohydrate increased the half life of polymeric IgG1, whereas absence of the carbohydrate in C_H2 accelerated the clearance rate.     

Functional genomics in rodent models of hypertension

Inbred strains of rodents have been used to study mammalian physiology and pathophysiology in an attempt to understand the contribution of genes in the pathogenesis of the disease process. In this review we focus on experimental animal models to identify quantitative trait loci (QTL) and possible strategies for identifying underlying genetic determinants responsible for hypertension. Confirmation of the existence of the QTL and dissection of the implicated region can be undertaken by production of either recombinant inbred, consomic or congenic strains. Despite complex interactions and the relatively few confirmed causative genes underlying QTL, recent developments in rat genome resources and advancement in statistical and bioinformatic methods will facilitate the identification of major gene(s) responsible for complex, polygenic traits.