IVIg selectively and rapidly decreases circulating pathogenic autoantibodies in pemphigus vulgaris

BACKGROUND: Intraveneous immunoglobulin (IVIg) is increasingly used to treat pemphigus vulgaris (PV). The mechanism by which it does so is not known. The following study was conducted to confirm the effectiveness of IVIg for the acute control of active PV and to elucidate the mechanism by which it does. METHODS: Twelve patients with active and severe PV unresponsive to conventional therapy with high doses of systemic steroids together with or without a cytotoxic drug were treated with a single dose of IVIg (400 mg/kg/day for 5 days). All patients were concurrently given cyclophosphamide or azathioprine of not already on one of these two drugs. The primary end-points were healing of skin lesions, changes in serum levels of intercelular (IC) autoantibodies and in steroid doses one to 3 weeks after initiation of IVIg. RESULTS: Within 1 week of initiating IVIg the activity of PV was controlled in most cases. Within 3 weeks the average baseline dose of systemic steroid was reduced by 40%. Serum levels of IC antibodies rapidly declined by an average of 59% within 1 week of initiating IVIg and by 70% within 2 weeks. The decrease was selective, as the average serum levels of antibody to varicella-herpes zoster did not decrease in the 4 patients in whom they were measured. The decrease in IC antibodies was inversely related to serum levels of total inmmunoglobulin (IgG). The decrease in IC antibodies was not due to blocking factors in the IVIg preparation and was too rapid to be due to suppression of IgG synthesis, suggesting that it resulted from increased catabolism. CONCLUSIONS: IVIg can rapidly control active PV unresponsive to conventional therapy by causing a selective and very rapid decline in the autoantibodies that mediate the disease. We believe it does so by increasing the catabolism of all serum IgG antibodies, and that this results in a selective decrease in only abnormal autoantibodies as catabolized normal anti bodies are replaced by those present in the IVIg preparation. IVIg is the first treatment that achieves the ideal therapeutic goal in auto-antibody diseases, the selective removal of the pathogenic antibodies without affecting the level of normal antibodies.     

Selection of the expressed B cell repertoire by infusion of normal immunoglobulin G in a patient with autoimmune thyroiditis

In the present study we have analyzed the changes in the expressed antibody repertoire and in temporal fluctuations of antibody levels in serum that followed infusion of normal IgG (IVIg) in a patient with autoimmune thyroiditis. Administration of IVIg resulted in the stimulation of IgM production, in alterations of expressed antibody activity in serum that could not merely be accounted for by the passive transfer of antibody specificities contained in IVIg, in transient down-regulation of B cells clones expressing a specific disease-related idiotype and in the increase in serum in recipient's autoantibodies specifically reactive with F(ab′)₂ fragments of IVIg. In addition, infusion of IVIg shifted the pattern of spontaneous fluctuations of autoantibody activities in the patient's serum from a pattern indicative of disconnected events in the immune network to a pattern similar to that which is consistently observed in healthy controls. These results suggest that normal IgG may modulate autoreactivity by selecting expressed antibody repertoire through V region-dependent interactions with antibodies.     

Immunoglobulin replacement in patients with chronic lymphocytic leukemia (CLL): Kinetics of immunoglobulin metabolism

Fifteen patients with low-grade B-cell tumours were given 3-weekly infusions for 1 year of intravenous immunoglobulin (IVIg) at a dose of 0.4 g/kg. Serial measurements of serum IgG levels were made; analysis of eight samples taken at intervals after the end of the last (17th) infusion showed that the half-life of IgG in such patients was no shorter than in normal individuals. To look at the average rates of catabolism of IgG during the year serum IgG was measured at four time points (pre, post, day 7, and day 21) after the 5th, 8th, 13th, and 17th infusions; these data showed that there were no changes in catabolism. Finally, there was a significant correlation (P<0.005) between the pretreatment serum IgG level and the increase to the mean trough level achieved after the fifth and subsequent infusions (in each individual). These data suggest that the catabolic rate of IgG is normal in patients with low-grade B-cell tumours and that it is not altered by regular IVIg infusions once a steady state is reached. Significant correlation of the increment of serum IgG with the endogenous synthesis level supports the theory that the IgG half-life is proportional to the IgG level at any given time.     

Reduction in serum levels of antimitochondrial (M2) antibodies following immunoglobulin therapy in severe combined immunodeficient (SCID) mice reconstituted with lymphocytes from patients with primary biliary cirrhosis (PBC)

The effect of gammaglobulin treatment on autoantibody production was investigated in SCID mice reconstituted with human peripheral blood mononuclear cells (PBMC) obtained from patients with PBC. All reconstituted mice displayed the presence of human antimitochondrial antibodies (αM2Ab) of both IgG and IgM types before treatment with human immunoglobulin. Two weeks after i.p. injection of 20 ×10⁶ PBMC into SCID mice, i.p. treatment with various preparations of human immunoglobulin was initiated. In control animals treated with saline, serum levels of human αM2Ab of the IgG type increased with time, peaking around 4 weeks after reconstitution. In contrast, human IgG autoantibodies rapidly decreased in all animals treated with human IgG. Treatment with a human IgM preparation had no effect on serum levels of αM2Ab of the IgG type. The results may suggest that the pronounced reduction of specific IgG autoantibodies was due to an increased catabolism of human IgG, including the autoantibodies, in the gammaglobulin-treated mice. Although the production of human αM2Ab in reconstituted mice could be easily shown, PBC-specific liver lesions or bile duct destruction were not observed, irrespective of treatment protocol.     

Serum or breast milk immunoglobulins mask the self‐reactivity of human natural IgG antibodies

B cells producing IgG antibodies specific to a variety of self‐ or foreign antigens are a normal constituent of the immune system of all healthy individuals. These naturally occurring IgG antibodies are found in the serum, external secretions, and pooled human immunoglobulin preparations. They bind with low affinity to antigens, which can also be targets for pathologic autoantibodies. An enhancement of naturally occurring IgG autoantibody activity was observed after treatment of human IgG molecules with protein‐destabilizing agents. We have investigated the interactions of human immunoglobulins that were obtained from serum or from breast milk of healthy individuals or IVIg with human liver antigens. Proteins from an individual serum or milk were isolated by two methods, one of which included exposure to low pH and the other did not. Purified serum, mucosal IgM, IgA, and the fraction containing immunoglobulin G F(ab’)₂ fragments each inhibited the binding of a single donor or pooled IgG to human liver antigens. Our study presents findings regarding the role of the breast milk or serum antibodies in blocking the self‐reactivity of IgG antibodies. It supports the suggestion that not IVIg only, but also the pooled human IgM and IgA might possess a potent beneficial immunomodulatory activity in autoimmune patients.     

Detection of antibodies to gangliosides and glycolipids in various intravenous immunoglobulin (IVIg) preparations

The aim of this study was to examine the presence of antibodies to GM1 and sulfatide in various IVIg preparations. Five brands of commercially available human IVIg (Sandoglobulin, Isiven, Cytogam, Omrigam and Cutter) were examined and compared. Serial dilutions of each of the above preparations were prepared at a working range of 0.009 to 25.0 mg/ml IVIg, and screened by a standard 96-well microplate EIA for autoantibodies to the ganglioside GM1 and to the glycolipid sulfatide. The various IVIg preparations (Omrigam, Cytogam, Sandoglobulin, Isiven), except for Cutter IVIg, contained low to medium titers of the autoantibodies tested. Omrigam and Cytogam IVIg contained low titer of antibodies to GM1, and medium-titer of antibodies to sulfatide, whereas Sandoglobulin and Isiven contained only low-titer of autoantibodies to sulfatide. The presence of natural autoantibodies to myelin in human sera may explain the presence of the tested antibodies within IVIg preparations. Measurements of antibodies to ganglioside and glycolipid in sera of Guillain-Barré patients immediately following IVIg, would probably not reveal antibody decrease. Alternatively, long-term (several weeks) follow-up of titers might result in their modification due to inhibition of antibodies production by IVIg.     

Antiidiotypic suppression of autoantibodies with normal polyspecific immunoglobulins

A mechanism by which therapeutic normal polyspecific immunoglobulins (IVIg) may suppress autoimmune responses in vivo is that of antiidiotypic suppression of autoantibodies mediated by anti-idiotypes present in IVIg. In vitro incubation with IVIg of either the plasma or the IgG fraction from plasma of patients with autoantibodies against procoagulant factor VIII (VIII:C), DNA, thyroglobulin, peripheral nerve and intrinsic factor resulted in dose-dependent inhibition of autoantibody activity. The pattern of inhibition curves showed a prozone phenomenon. Maximal inhibition was achieved at a ratio of patient's IgG to IVIg which was specific for each antibody tested. Inhibition was dependent on idiotypic/antiidiotypic interactions between autoantibodies and IVIg since: 1) F(ab')2 from IVIg inhibited autoantibody activity in F(ab')2 fragments from patients' IgG; 2) IVIg contained no antigen-like activity and no antibodies against the commonest allotypes expressed in F(ab')2 fragments of human IgG; 3) autoantibody activity in F(ab')2 fragments from patients' IgG was specifically retained on affinity columns of Sepharose-bound F(ab')2 fragments from IVIg. The presence of antiidiotypes against autoantibodies in pooled normal IgG supports the concept of a functional idiotypic network regulating autoimmune responses in man.     

Idiotypic and anti-idiotypic elastin autoantibodies: Implications for IVIg and pregnancy loss

PROBLEM: The aim of this study was to investigate anti-elastin and anti-anti-elastin autoantibodies in intravenous immunoglobulin (IVIg) lots as an attempt to further explain the effect of IVIg in recurrent pregnancy loss (RPL). METHOD OF STUDY: Serum samples of 10 female patients with RPL and 10 healthy subjects were tested for anti-elastin autoantibodies and used in competitive inhibition studies. A total of 44 IVIg lots (ZLB Behring, Switzerland) were tested for anti-elastin and anti-anti-elastin idiotypes. One way analysis of variance (ANOVA) and Least Significant Difference (LSD method) were used for statistical analysis of differences between the lots. RESULTS: Serum anti-elastin IgG autoantibodies were significantly higher in the study group, compared to the controls. In all lots anti-elastin IgG antibodies were identified. All lots (except two of them) showed similar dose-dependent inhibition of serum anti-elastin activity by anti-elastin anti-idiotypes in IVIg. CONCLUSIONS: Anti-elastin IgG autoantibodies were increased in patients with RPL - a finding which needs further explanation. Anti-elastin and anti-anti-elastin idiotypes were identified in different IVIg lots. The presence in IVIg of anti-idiotypes against anti-elastin autoantibodies from patients' sera could be an additional mechanism of the beneficial effect of IVIg in reproductive failure.     

Novel mechanisms of target cell death and survival and of therapeutic action of IVIg in Pemphigus

Pemphigus vulgaris (PV) is a potentially lethal mucocutaneous blistering disease characterized by cell-cell detachment within the stratified epithelium (acantholysis) caused by IgG autoantibodies. Intravenous immunoglobulin (IVIg) therapy effectively treats PV, but the mechanism is not fully understood. To further understand acantholysis and the efficacy of IVIg, we measured effects of IgG fractions from PV patients on keratinocyte death processes. Using IgGs from representative PV patients who improved with IVIg, we identified apoptotic and oncotic signaling pathways in in vitro and in vivo PV models. We identified two groups of PV patients, each producing autoantibodies activating predominantly either apoptotic or oncotic cell death pathway. Experimental treatments with caspase 3 or calpain inhibitors demonstrated that PV IgGs induced acantholysis through both pathways. Upstream, the apoptotic signaling involved activation of caspases 8 and 3 and up-regulation of Fas ligand mRNA, whereas calpain-mediated cell death depended on elevated intracellular free Ca(2+). IVIg reduced PV IgG-mediated acantholysis and cell death and up-regulated the caspase inhibitor FLIP and the calpain inhibitor calpastatin. These results indicate that in different PV patients, IgG-induced acantholysis proceeds predominantly via distinct, yet complementary, pathways of programmed cell death differentially mediated by apoptosis and oncosis effectors, with IVIg protecting target cells by up-regulating endogenous caspase and calpain inhibitors.     

IgE Antibodies in Sera from Patients with Bullous Pemphigoid Are Autoantibodies Preferentially Directed Against the 230-kDa Epidermal Antigen (BP230)

Bullous pemphigoid (BP) is unique among autoimmune skin diseases in which a high serum IgE level has been detected. We sought to determine the antigenic specificity of these IgE antibodies in 39 BP sera by immunofluorescence microscopy, immunoblot, and ELISA. The patient's sera contained IgG antibodies to 230-kDa (BP230) (n = 20), 180-kDa (BP180) (n = 9), and both BP230 and BP180 (n = 10) antigens. Serum IgE levels varied from 29 to 5000 kIU/L (mean ± SD, 856 ± 1426 kIU/L), among which sera containing IgG antibodies to BP230 had an IgE level on average 4.3 times higher than anti-BP180 sera. IgE antibodies in 18 sera were found to be autoantibodies reactive either with an epidermal component of basement membrane zone by immunofluorescence microscopy on 1 M NaCl-split skin or with a 230-kDa antigen by immunoblots of cultured human keratinocytes.⁷ The 230-kDa epidermal antigen recognized by IgE antibodies comigrated with the BP230 as labeled by a specific human monoclonal antibody. IgE anti-BP230 antibodies in patients' sera were always associated with IgG autoantibodies. No sera contained IgE antibodies to BP180 or to any other epidermal or dermal antigens as verified by immunoblot and ELISA. A good correlation was found between the presence of IgE circulating autoantibodies and the level of serum IgE (P < 0.004). IgE antibodies to BP230, like IgG autoantibodies, were mapped primarily to the C-terminal end of the protein, as they labeled rBP55, a BP230 recombinant protein encoded by a cDNA for the C-terminal end of BP230.     

Anti-idiotypes against anti-neutrophil cytoplasmic antigen autoantibodies in normal human polyspecific IgG for therapeutic use and in the remission sera of patients with systemic vasculitis.

Anti-neutrophil cytoplasmic antigen (ANCA) activity was inhibited in 15 out of 21 sera from patients with acute systemic vasculitis following incubation with normal polyspecific IgG for therapeutic use (IVIg). ANCA antibodies reacted with IVIg through idiotypic-anti-idiotypic interactions, as shown in competitive binding assays using F(ab')2 fragments from IVIg and affinity chromatography of ANCA IgG on Sepharose-bound F(ab')2 fragments from IVIg. Co-incubation of sera from patients with acute systemic vasculitis with paired autologous remission stage sera also resulted in inhibition of ANCA activity in acute sera. Remission sera contain IgM and IgG capable of interacting with beta and or alpha idiotypes of ANCA IgG from acute sera. Anti-idiotypic IgM may account for the lack of expression of ANCA activity in whole serum from patients in remission from systemic vasculitis, which were found to contain high titres of ANCA IgG. These observations suggest that remission of systemic vasculitis is associated with the generation of anti-idiotypes against autoantibodies rather than the suppression of production of ANCA autoantibodies. IVIg may modulate the activity of systemic vasculitis in vivo.     

Idiotypic interactions between normal human polyspecific IgG and natural IgM antibodies

Pooled normal human polyspecific IgG (IVIg) contain anti-idiotypes against a variety of autoantibodies from patients with autoimmune diseases and IgG autoantibodies present in IVIg. The present study indicates that IVIg may also react through idiotypic/anti-idiotypic interactions with human natural IgM antibodies. Sixty-four percent of IgM secreted by B lymphoid cell lines derived from B cells of healthy elderly donors and 18% of IgM secreted by cloned EBV-transformed cord B cells that were tested, bound through their variable region to F(ab')2 fragments of IVIg. The binding to 2,4,6-trinitrophenyl (TNP) of a polyreactive IgM with anti-TNP specificity, was inhibited by F(ab')2 fragments from IVIg, indicating the presence in IVIg of anti-idiotypes that may interfere with the antibody-combining site of polyreactive IgM antibodies. The ability of IgM antibodies to interact with idiotypes on IVIg was not related to the degree of polyreactivity of natural antibodies. Our observations further document that IVIg contain antibody specificities against Ig from normal individuals and suggest that IgG originating from the physiologically expressed repertoire may modulate the expression of the potential B cell repertoire. The results may be relevant to the suppressive effect of IVIg in autoimmune diseases.     

Intravenous immunoglobulin preparations have no direct effect on B cell proliferation and immunoglobulin production

Intravenous immunoglobulin (IVIg) is used for treatment of a variety of immunological disorders and in transplantation. As one of its applications in transplantation is the reduction of donor specific antibodies in the circulation, we examined the direct effect of IVIg on essential parameters of human B cell responses in vitro. Purified human B cells, human B cell hybridomas and T cells were cultured in the presence of graded concentrations of IVIg to test its effect on their proliferative capacity. To address the effect of IVIg on immunoglobulin production, we designed a novel technique making use of quantitative polymerase chain reaction to assess IgM and IgG levels. IVIg failed to inhibit proliferation of human B cells and human B cell hybridomas. In contrast, when IVIg was added to T cell cultures, a dose‐dependent reduction of the proliferative capacity was observed. IVIg did not affect the levels of IgM and IgG mRNA of activated B cells. Our data show that IVIg is not capable of directly inhibiting key B cell responses. Direct B cell inhibition by IVIg seems therefore unlikely, implying that alteration in humoral immunity by IVIg is due to indirect effects on T cells and/or interactions with circulating antibodies and complement factors.     

Elimination of Infectious Antigens and Increase of IgG Catabolism as Possible Modes of Action of IVIg

Many mechanisms can explain the mode of action of IVIg in immune disorders. Macrophage blockade and interference in the idiotypic network are supported by some experimental data. Among the other mechanisms, two are considered in greater detail. Firstly, in some disorders, the patients could improve simply because the infused Ig contains antibodies directed against the infectious antigen causing the disease. Secondly, one can expect that IVIg increases the IgG catabolism and therefore the elimination of the autoantibodies. When the concentration of IgG in the plasma reaches 200% of the normal value, for example, the fractional catabolic rate increases up to 180% of its normal value. In other words, the half-life of IgG is decreased from 21 days to 12 days.     

A monoclonal anti-idiotypic antibody against the antigen-combining site of anti-factor VIII autoantibodies defines and idiotope that is recognized by normal human polyspecific immunoglobulins for therapeutic use (IVIg).

The present study demonstrates that normal human immunoglobulins for therapeutic use (IVIg) contain anti-idiotypes that recognize an antigen-binding site-related idiotope of anti-Factor VIII autoantibodies defined by a mouse monoclonal antibody (MoAb). MoAb 20F2 was obtained by immunizing a mouse with affinity-purified anti-Factor VIII F(ab')2 fragments prepared from the IgG fraction of a patient with anti-Factor VIII autoantibodies. The monoclonal antibody was directed against an overlapping epitope on the antigen-binding site of the patient's anti-Factor VIII autoantibodies and the CH1 domain of human IgG1. The anti-Factor VIII activity of the patients's autoantibodies was neutralized by MoAb 20F2 in a dose-dependent manner. A fraction of the patient's anti-Factor VIII auto-antibodies was specifically retained on affinity columns of Sepharose-bound MoAb 20F2; anti-Factor VIII activity of antibodies in this fraction was totally inhibited by MoAb 20F2, indicating an idiotopic homogeneity of retained anti-Factor VIII autoantibodies. IVIg inhibited the anti-Factor VIII activity of 20F2 idiotope-positive F(ab')2 antibodies, thus indicating that the IVIg recognize the 20F2 idiotope on patient's autoantibodies. These observations further support the concept of the presence in IVIg of anti-idiotypes against autoantibodies associated with human autoimmune diseases.     

Anti-argonaute2 (Ago2/Su) and -Ro antibodies identified by immunoprecipitation in primary anti-phospholipid syndrome (PAPS)

Objectives. Primary anti-phospholipid syndrome (PAPS) is an autoimmune condition defined by anti-phospholipid antibodies (aPL) and thrombotic or obstetric events. Some PAPS can evolve into systemic lupus erythematosus (SLE) during follow-up. Few studies systematically examined lupus autoantibodies and their clinical significance in PAPS. The aim of our study is to analyze the clinical and laboratory correlations with lupus-related autoantibodies, detected by immunoprecipitation (IP), a technique not yet systematically applied to investigate autoantibodies in this condition.

Methods. Sera from 52 PAPS patients were screened by indirect immunofluorescence (IIF) antinuclear antibodies (ANA), IP of ³⁵S-labeled K562 cell extract, and ELISA [anti-Argonaute2 (Ago2, Su), 60kRo, 52kRo, La, dsDNA)]. Anti-Ago2/Su positive sera were also tested for anti-GW bodies (GWBs) by IIF double staining, using rabbit anti-Rck/p54 serum.

Results. First, 56% of PAPS patients (29/52) were ANA positive, mainly with speckled pattern. Anti-Ago2/Su antibodies were found in 13% (7/52), anti-Ro/SSA in 10% (5/52), anti-La in one case. The clinical profile of patients did not seem to be related to the presence of these antibody specificities. However, levels of IgG anti-β2 glycoprotein I antibodies were lower in anti-Ago2/Su positive patients (p = 0.02). None of anti-Ago2/Su or —Ro patients developed SLE during a 2-year follow-up. Ago2 is a key component of GWBs, however, only 1/7 anti-Ago2/Su serum showed a typical cytoplasmic GWBs staining.

Conclusions. Anti-Ago2/Su and -Ro antibodies are the two autoantibodies detected by IP in our PAPS cohort. Clarifying why Ago2/Su and Ro are specific targets of autoimmunity may help to understand the mechanisms of autoantibody production.     

A V region-connected autoreactive subfraction of normal human serum immunoglobulin G.

Mouse and human natural IgM autoantibodies have been shown to be polyreactive and "connected" through V region-dependent interactions. In the present study, we have identified a connected subfraction of normal human serum IgG by using affinity chromatography of F(ab')2 fragments of pooled IgG (IVIg) or of IgG from a single donor on Sepharose-bound F(ab')2 fragments of the same source of IgG. The connected fraction of IgG exhibited a high content of autoantibodies directed against a wide panel of evolutionarily conserved self antigens and of self antigens that may be targets of autoantibodies in autoimmune diseases. Connected IgG also contained higher amounts of antibodies directed against commonly encountered microbial antigens than unfractionated IgG. The connected fraction did not, however, differ from unchromatographed IgG nor from non-connected IgG in its content of antibodies to vaccinal antigens and to distant foreign antigens. Thus, in humans as in mice, connectivity is a prominent feature of autoantibodies. Our observations are suggestive of a tight control by IgG of the expressed autoreactive repertoire in healthy individuals and strengthen the concept that the therapeutic infusion of pooled normal IgG (IVIg) may be effective in autoimmune diseases by bringing to patients normal regulatory components of the immunoglobulin network.     

Immunoglobulin (Ig)G purified from human sera mirrors intravenous Ig human leucocyte antigen (HLA) reactivity and recognizes one's own HLA types,but may be masked by Fab complementarity‐determining region peptide in the native sera

Intravenous immunoglobulin (IVIg) reacted with a wide array of human leucocyte antigen (HLA) alleles, in contrast to normal sera, due possibly to the purification of IgG from the pooled plasma. The reactivity of IgG purified from normal sera was compared with that of native sera to determine whether any serum factors mask the HLA reactivity of anti‐HLA IgG and whether IgG purified from sera can recognize the HLA types of the corresponding donors. The purified IgG, unlike native sera, mirrored IVIg reactivity to a wide array of HLA‐I/‐II alleles, indicating that anti‐HLA IgG may be masked in normal sera – either by peptides derived from soluble HLA or by those from antibodies. A < 3 kDa peptide from the complementarity‐determining region (CDR) of the Fab region of IgG (but not the HLA peptides) masked HLA recognition by the purified IgG. Most importantly, some of the anti‐HLA IgG purified from normal sera – and serum IgG from a few donors – indeed recognized the HLA types of the corresponding donors, confirming the presence of auto‐HLA antibodies. Comparison of HLA types with the profile of HLA antibodies showed auto‐HLA IgG to the donors' HLA antigens in this order of frequency: DPA (80%), DQA (71%), DRB345 (67%), DQB (57%), Cw (50%), DBP (43%), DRB1 (21%), A (14%) and B (7%). The auto‐HLA antibodies, when unmasked in vivo, may perform immunoregulatory functions similar to those of therapeutic preparations of IVIg.     

Mercury induces polyclonal B cell activation,autoantibody production and renal immune complex deposits in young (NZB × NZW)F1 hybrids

It is well established that in susceptible mouse strains, chronic treatment with subtoxic doses of mercuric chloride (HgCl₂) induces a systemic autoimmune disease, which is characterized by increased serum levels of IgG1 and IgE antibodies, by the production of anti-nucleolar antibodies and by the development of immune complex-mediated glomerulonephritis. Susceptibility to mercury is partly under the control of major histocompatibility complex genes. To study the susceptibility to mercury further, we investigated the in vivo effects of mercury in young autoimmune disease prone (NZB × NZW)F1 (H-2^d/z) mice prior to establishment of spontaneous autoimmune disease. Mercury-susceptible SJL (H-2^s) mice and mercury low-responder BALB/c (H-2^d) mice were used as positive and negative controls, respectively. In (NZB × NZW)F1 mice, treatment with mercury stimulated an intense antibody formation characterized by increased numbers of splenic IgG1 and IgG3 antibody-producing cells as well as by elevated serum IgE levels. Injection with mercury also induced an increased production of IgG1, IgG2b and IgE antibodies in SJL, but not in BALB/c mice. The mercury-induced IgG1 response in (NZB × NZW)F1 and SJL mice was found to be polyclonal and autoantibodies against double-stranded (ds)DNA, IgG, collagen, cardiolipin, phosphatidylethanolamine as well as antibodies against the hapten trinitrophenol were produced. In addition, SJL, but not (NZB × NZW)F1 or BALB/c mice, produced IgG1 anti-nucleolar antibodies after treatment with mercury. Further studies demonstrated that (NZB × NZW)F1 and SJL mice developed high titers of renal mesangial immune complex deposits containing IgG1 antibodies 3 weeks after injection with mercury. Thus, a mouse strain genetically prone to develop spontaneous autoimmune diseases is highly susceptible to mercury-induced immunopathological alterations.     

The immune response to influenza virus: III. Changes in the avidity and specificity of early IgM and IgG antibodies

Serum samples taken from rabbits 5 days after vaccination with SW influenza virus by the intravenous route contained high levels of IgM antibodies. IgG antibodies were either not detected or were present at very low levels. By the 10th day after vaccination both IgM and IgG antibodies were present in the serum. The early IgM antibodies were of high avidity while the early IgG antibodies were of very low avidity. The presence of low avidity IgG antibodies in whole serum caused a decrease in the average avidity of the antibodies in whole serum from the 5th to the 10th day post vaccination. The avidity of the IgM antibodies remained fairly constant for the first 20 days of the immune response but a slight increase was detected after secondary vaccination. The avidity of the early IgG antibodies increased during the test period of 20 days. The early IgM and IgG antibodies were heterogeneous with respect to avidity.

The highly avid IgM antibodies showed high cross-reactivity with related influenza viruses, i.e. they were of low specificity. The early IgG antibodies that were of low avidity cross-reacted with only one other influenza virus out of the four tested, i.e. they were more specific; as the avidity of the IgG antibodies increased so did their cross-reactivity.