Induction of rheumatoid antibodies in the mouse. Regulated production of autoantibody in the secondary humoral response

Rheumatoid factor IgM autoantibodies control IgG homeostasis

Rheumatoid arthritis is an autoimmune disease characterized by joint inflammation due to autoantibodies targeting multiple self-proteins. Most patients with poor prognosis show elevated titers of IgM antibodies specifically binding to IgG. Such autoreactive antibodies are referred to as rheumatoid factor (RF). However, their biological function and contribution to disease progression remains elusive. We have recently shown that autoreactive antibodies are present in healthy individuals and play an important role in regulating physiological processes. This regulatory mechanism is determined by the class and affinity of the autoreactive antibody, as low-affinity autoreactive IgM neutralizes the recognized autoantigen while high-affinity IgM protects its autoantigen from degradation. Here, we show that RFs possessing a high affinity and mono-specificity to IgG have a stabilizing effect on IgG, whereas low-affinity polyreactive RFs neutralize IgG in vivo. These results suggest that autoreactive IgM antibodies recognizing IgG play a crucial role in regulating IgG homeostasis and that a disbalance between IgM-mediated IgG degradation and stabilization might affect the onset and progression of autoimmune diseases. Consequently, restoring this balance using low-affinity anti-IgG IgM might be a promising therapeutic approach for autoimmune diseases involving autoreactive IgG.

Safety of Multiple Vaccinations and Durability of Vaccine-Induced Antibodies in an Italian Military Cohort 5 Years after Immunization

We previously examined the safety and immunogenicity of multiple vaccines administered to a military cohort, divided into two groups, the first composed of students at military schools, thus operating inside the national borders for at least 3 years, and the other formed of soldiers periodically engaged in a 9-month-long mission abroad (Lebanon). In the current study, we analyzed 112 individuals of this cohort, 50 pertaining to the first group and 62 to the second group, in order to examine the possible late appearance of side effects and to calculate the half-life of the induced antibodies. Moreover, the possible involvement of B-cell polyclonal activation as a pathogenetic mechanism for long term antibody persistence has even been explored. No late side effects, as far as autoimmunity and/or lymphoproliferation appearance, have been noticed. The long duration of the vaccine induced anti-HAV antibodies has been confirmed, whereas the antibodies induced by tetravalent meningococcal polysaccharide vaccine have been found to persist above the threshold for putative protection for a longer time, and anti-tetanus, diphtheria, and polio 1 and 3 for a shorter time than previously estimated. No signs of polyclonal B-cell activation have been found, as a possible mechanism to understand the long antibody persistence.

Fra1 Controls Rheumatoid Factor Autoantibody Production by Bone Marrow Plasma Cells and the Development of Autoimmune Bone Loss

Next to proinflammatory cytokines, autoimmunity has been identified as a key trigger for osteoclast activation and bone loss. IgG-rheumatoid factor (IgG-RF) immune complexes, which are present in patients with rheumatoid arthritis, were shown to boost osteoclast differentiation. To date, the regulation of IgG-RF production in the absence of inflammatory triggers is unknown. Herein, we describe Fra1 as a key checkpoint that controls IgG-RF production by plasma cells and regulates autoimmune-mediated bone loss. Fra1 deficiency in B cells (Fra1^ΔBcell ) led to increased IgG1-producing bone marrow plasma cells, enhanced IgG-RF production, and increased bone loss associated with elevated osteoclast numbers after immunization. The effect of IgG-RF on osteoclasts in vitro and on osteoclasts associated with bone loss in vivo was dependent on FcγR, especially FcγR3. Furthermore, immunization of WT mice with T-cell-dependent antigens induced a significant and robust decrease in Fra1 expression in bone marrow B cells, which was followed by increased IgG1 production and the induction of osteoclast-mediated bone loss. Overall, these data identify Fra1 as a key mediator of IgG-RF production and autoimmune-mediated bone loss. © 2019 American Society for Bone and Mineral Research.

Anti-carbamylated protein antibodies precede disease onset in monkeys with collagen-induced arthritis

Background

Rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA) and anti-carbamylated protein (anti-CarP) antibodies are rheumatoid arthritis (RA)-associated autoantibodies. Besides their presence in human serum, anti-CarP antibodies have also been described in rodent models of arthritis, while ACPA are not consistently detectable. Data on these RA-associated autoantibodies in primates are not available. Therefore, we investigated the presence of RF, anti-CarP antibodies and ACPA in rhesus monkeys before and after collagen-induced arthritis immunizations.

Methods

In previous studies, arthritis was induced in groups of rhesus monkeys by immunisation with collagen following pre-treatment with placebo, abatacept or Roactemra. Previously collected serum was used to measure, autoantibodies by ELISA, detecting anti-CarP antibodies, RF-IgM and antibodies against CCP2, citrullinated myelin basic protein and citrullinated fibrinogen.

Results

Out of the three autoantibodies, only anti-CarP antibodies were detectable in resus monkeys with arthritis. RF-IgM and ACPA were undetectable and below the detection limit of the ELISA. The level of anti-CarP antibodies increases over time and, similar to in humans and mice, these autoantibodies were already detectable before clinical disease onset. Furthermore, preventive treatment with abatacept (CTLA4/IgG1-Fc fusion protein) inhibited the development of anti-CarP antibodies after immunization, while this was less evident for preventive Roactemra (anti-IL6-receptor) treatment. Moreover, disease progression was only reduced following abatacept treatment.

Conclusion

Rhesus monkeys develop anti-CarP antibodies upon induction of collagen-induced arthritis, while we were unable to detect RF or ACPA. Also, the development of anti-CarP antibodies could be inhibited by preventive abatacept treatment.

Lack of evidence for post-vaccine onset of autoimmune/lymphoproliferative disorders, during a nine-month follow-up in multiply vaccinated Italian military personnel

Anecdotal case reports, amplified by mass media and internet-based opinion groups, have recently indicated vaccinations as possibly responsible for autoimmunity/lymphoproliferation development. Multiply vaccinated Italian military personnel (group 1, operating in Italy, group 2, operating in Lebanon) were followed-up for nine months to monitor possible post-vaccine autoimmunity/lymphoproliferation onset. No serious adverse event was noticed in both groups. Multivariate analysis of intergroup differences only showed a significant association between lymphocyte increase and tetanus/diphtheria vaccine administration. A significant post-vaccine decrease in autoantibody positivity was observed. Autoantibodies were also studied by microarray analysis of self-proteins in subjects exposed to ≥4 concurrent vaccinations, without observing significant difference among baseline and one and nine months post-vaccine. Moreover, HLA-A2 subjects have been analyzed for the possible CD8T-cell response to apoptotic self-epitopes, without observing significant difference between baseline and one month post-vaccine. Multiple vaccinations in young adults are safe and not associated to autoimmunity/lymphoproliferation onset during a nine-month-long follow-up.

Elevated levels of antibodies against xenobiotics in a subgroup of healthy subjects

In spite of numerous research efforts, the exact etiology of autoimmune diseases remains largely unknown. Genetics and environmental factors, including xenobiotics, are believed to be involved in the induction of autoimmune disease. Some environmental chemicals, acting as haptens, can bind to a high-molecular-weight carrier protein such as human serum albumin (HSA), causing the immune system to misidentify self-tissue as an invader and launch an immune response against it, leading to autoimmunity. This study aimed to examine the percentage of blood samples from healthy donors in which chemical agents mounted immune challenges and produced antibodies against HSA-bound chemicals. The levels of specific antibodies against 12 different chemicals bound to HSA were measured by ELISA in serum from 400 blood donors. We found that 10% (IgG) and 17% (IgM) of tested individuals showed significant antibody elevation against aflatoxin-HSA adduct. The percentage of elevation against the other 11 chemicals ranged from 8% to 22% (IgG) and 13% to 18% (IgM). Performance of serial dilution and inhibition of the chemical–antibody reaction by specific antigens but not by non-specific antigens were indicative of the specificity of these antibodies. Although we lack information about chemical exposure in the tested individuals, detection of antibodies against various protein adducts may indicate chronic exposure to these chemical haptens in about 20% of the tested individuals. Currently the pathological significance of these antibodies in human blood is still unclear, and this protein adduct formation could be one of the mechanisms by which environmental chemicals induce autoimmune reactivity in a significant percentage of the population.

Molecular basis for the cross-reactive idiotypes on human anti-IgG autoantibodies (rheumatoid factors)

High titres of anti-IgG autoantibodies (rheumatoid factors, RF) are characteristic of patients with rheumatoid arthritis, Sjögren's syndrome, and mixed cryoglobulinaemia, and may contribute to immune complex formation and tissue damage. The monoclonal RFs from cryoglobulinaemia patients frequently display cross-reactive idiotypes. The genetic basis for the cross-reactive idiotypes on RF autoantibodies has not been determined. To clarify structural and genetic relationships among RFs from unrelated subjects, a series of anti-peptide antibodies have been generated that define primary sequence-dependent idiotypes on RF heavy and light chains. Multiple monoclonal and polyclonal RFs from unrelated individuals have been probed by Western blotting with the anti-idiotypic reagents. The results show that sequences in the kappa light chain variable region represent a common structural element among RF autoantibodies. This hypothesis is confirmed by the cloning and sequencing of the conserved germline variable region gene which encodes human RF kappa chains.

B Cell Tolerance Checkpoints That Restrict Pathways of Antigen-Driven Differentiation

Autoreactive B cells can be regulated by deletion, receptor editing, or anergy. Rheumatoid factor (RF)-expressing B lymphocytes in normal mice are not controlled by these mechanisms, but they do not secrete autoantibody and were presumed to ignore self-Ag. Surprisingly, we now find that these B cells are not quiescent, but instead are constitutively and specifically activated by self-Ag. In BALB/c mice, RF B cells form germinal centers (GCs) but few Ab-forming cells (AFCs). In contrast, autoimmune mice that express the autoantigen readily generate RF AFCs. Most interestingly, autoantigen-specific RF GCs in BALB/c mice appear defective. B cells in such GCs neither expand nor are selected as efficiently as equivalent cells in autoimmune mice. Thus, our data establish two novel checkpoints of autoreactive B cell regulation that are engaged only after initial autoreactive B cell activation: one that allows GCs but prevents AFC formation and one that impairs selection in the GC. Both of these checkpoints fail in autoimmunity.

Rheumatoid factor-like IgM in Plasmodium berghei (Apicomplexa: Haemosporida) infections of BALB/c mice

Groups of female BALB/c mice infected by intravenous injection with 50 erythrocytes containing Plasmodium berghei Vincke et Lips, 1948 were sacrificed on days 3 through 12 after infection. Rheumatoid factor-like IgM (RF-IgM) and parasite-specific IgG levels were determined by enzyme-linked immunosorbent assay in serum specimens and in culture medium removed from spleen cell cultures established at sacrifice. All four mouse IgG subisotypes were recognized by RF-IgM molecules induced by Plasmodium berghei infection, and in this regard, the parasite-induced RF-IgM response resembled that induced by lipopolysaccharide polyclonal activation. Plasmodium berghei infection resulted in a biphasic RF-IgM response, with infected animals demonstrating significantly increased levels of RF-IgM early in the infection and significantly decreased levels late in the infection, compared to uninfected control mice. The decreased levels of RF-IgM observed late in infection correlated with increasing parasitaemia levels, and were primarily due to a decrease in RF-IgM specific for mouse IgG2a. Late infection levels of RF-IgM specific for IgGI, IgG2b, and IgG3 were not significantly different from those of control animals.

From T to B and back again: positive feedback in systemic autoimmune disease

Systemic lupus erythematosus, a prototypical systemic autoimmune disease, is the result of a series of interactions within the immune system that ultimately lead to the loss of self-tolerance to nuclear autoantigens. Here, we present an integrated model that explains how self-tolerance is initially lost and how the loss of tolerance is then amplified and maintained as a chronic autoimmune state. Key to this model are the self-reinforcing interactions of T and B cells, which we suggest lead to perpetuation of autoimmunity as well as its spread to multiple autoantigen targets.

Dimensions of antigen recognition and levels of immunological specificity

Although recognition and specificity are among the most fundamental concepts in immunology, there is a common tendency to equate these notions with the fit, especially in terms of molecular shape, between interacting molecules. Even in the case of monovalent recognition, there are factors that contribute to the energetics of the interaction that are not readily accounted for by detailed structural analysis of the interacting (epitopic and paratopic) molecular surfaces. Consequently, recognition involves more than just the three spatial dimensions and time. Factors such as solute-solvent interactions, molecular crowding, and confinement, not directly related to the details of the intermolecular interface, can play crucial roles in determining both intrinsic affinity and differential intrinsic affinity. Furthermore, stating that a given structural subunit (e.g., amino acid) is recognized in a given noncovalent interaction does not clarify whether the structural subunit in question participates in the interaction through van der Waals contact, contribution to intrinsic affinity, or differential contribution to relative intrinsic affinities for two or more different ligands. Additional factors become relevant in considering the specificity exhibited in multivalent interactions, cell activation, and activation of the whole immune system. Therefore, specificity as defined for a monovalent binding event can diverge from specificity as it is defined for higher-order interactions. A corollary of this conclusion is that the composition of epitopes and paratopes, defined in terms of the structural elements for which substitutions have an effect on the specificity-defining measurement, can differ in different contexts despite complete conservation of the structures that physically make direct contact. An analysis of specificity at the organismal level suggests that the immune system does not recognize or respond to substances that correspond precisely to either nonself substances or to dangerous substances. An alternative notion for the molecular origins of immunological discrimination does not require that there be any single reason for immune responsiveness. This concept of what the immune system recognizes and responds to derives from the recognition that the ultimate function of the immune system is to contribute to survival and reproductive success through any available means.

Evidence that human immunoglobulin M rheumatoid factors can Be derived from the natural autoantibody pool and undergo an antigen driven immune response in which somatically mutated rheumatoid factors have lower affinities for immunoglobulin G Fc than their germline counterparts

The question of whether immunoglobulin (Ig)M rheumatoid factors (RF) arise as the result of an abnormal expansion of already existing clones producing natural autoantibodies or emerge as new clones that are somatically mutated owing to an antigen driven immune response has never been conclusively answered. In this study, an inhibition ELISA was utilized to measure the affinities of recombinant antibodies using VH segments reverted back to their closest germline counterparts (germline revertants). In all cases, the somatically mutated parental RFs had a decreased affinity for immunoglobulin (Ig)G Fc compared to the germline revertant, indicating that the antibodies in the germline configuration had the higher affinities. This demonstrates that somatic mutation is not a prerequisite to generate disease associated antibodies. The presence of mutations in the parental IgM RFS suggests that these cells had been involved in a germinal centre reaction. As the germinal centre is the conventional site of the acquisition of mutations during an antigen driven response, these data suggest a role for germinal centres in the generation of the antibody diversity in addition to the selection of higher affinity antibodies. Assuming that only antigen selected cells survive deletion, these data support the hypothesis that IgM RFS can be derived from the natural autoantibody repertoire and result from an antigen driven response. Mechanisms controlling the survival of B cells based on the affinity/avidity of the immunoglobulin receptor are shown to be functional in patients with rheumatoid arthritis.

Histidine-rich glycoprotein prevents the formation of insoluble immune complexes by rheumatoid factor

In previous studies we have shown that histidine-rich glycoprotein (HRG), a relatively abundant plasma protein, can bind to immunoglobulin G (IgG) and inhibit the insolubilization of IgG-containing immune complexes (IC). It was of interest, therefore, to determine whether HRG can inhibit the formation of insoluble IC (IIC) resulting from the interaction of rheumatoid factor (RF) with human IgG-containing IC. Light scattering techniques were used to examine the effect of HRG on the formation of IIC between RF and IC containing human IgG according to three different models. In all three models physiological concentrations of HRG could block the formation of IIC induced by RF. Optical biosensor studies of the RF-IgG interaction also revealed that HRG can mask the epitopes on IgG recognized by RF. Additional studies examined whether HRG can solubilize already formed IIC and demonstrated that HRG can, in fact, partially solubilized IIC. These data indicate that HRG can regulate the formation of IIC induced by RF at three levels: namely by inhibiting the initial recognition of IgG containing IC by RF, by inhibiting the subsequent insolubilization of IgG containing IC by RF and by solubilizing already formed IIC. Collectively, these findings suggest that HRG may be an important inhibitor of the formation of pathogenic IC in diseases such as systemic lupus erythematosus and rheumatoid arthritis.

Growing up on the streets: why B-cell development differs from T-cell development

B-cell development differs significantly from T-cell development in that negative selection of autoreactive B cells can occur in the same microenvironment in which productive immune responses begin. Here, Sarah Townsend and colleagues discuss how this 'growing up on the streets' might provide a mechanism that fills holes in the B-cell repertoire, much as major histocompatibility complex polymorphism fills holes in the T-cell repertoire.

Maternal Ig Mediates Neonatal Tolerance in Rheumatoid Factor Transgenic Mice but Tolerance Breaks Down in Adult Mice

We have recently demonstrated that B cell deletion occurs in the bone marrow of IgHa high affinity anti-IgG2aa (RF) transgenic mice. Here we demonstrate via genetic crosses that the source of IgG2a is the mother, thus establishing a transplacental mechanism that ensures tolerance to developmentally expressed Ags. Since maternal IgG can mediate tolerance in young mice, whether tolerance is maintained or, instead, autoimmunity ensues after weaning was investigated. We find that deletion remits abruptly in these RF transgenic mice beginning at 2 to 3 wk postweaning, and some degree of autoreactivity can be observed thereafter for weeks to months. The mechanism of sustained expression of autoreactive RF B cells in normal mice is unclear as yet, but a plausible mechanism is that once self-reactive cells are present, the antibody they secrete markedly reduces the autoantigen levels, presumably allowing further development, rather than deletion, of newly arising B lineage cells. The phenotype of these RF transgenic mice suggests a positive feedback mechanism that tends to perpetuate autoimmunity once it has been established. If such a mechanism were to exist in autoimmune animals, it could have important implications for the establishment and maintenance of B and T cell tolerance in chronic autoimmune diseases.

Peripheral deletion of rheumatoid factor B cells after abortive activation by IgG

Rheumatoid factor (RF) B cells proliferate during secondary immune responses to immune complexed antigen and antigen specific T cells, but higher affinity RFs are not detected except in patients with rheumatoid arthritis and other autoimmune diseases. Consequently, there must exist highly efficient mechanisms for inactivation of these higher-affinity RF B cell clones under normal circumstances. Exposure of transgenic mice expressing a human IgM RF to soluble human IgG in the absence of T cell help causes antigen specific B cell deletion in 2-3 days. The deletion is independent of the Fas/Fas ligand (FasL) pathway of apoptosis and is preceded by a phase of partial activation involving increase in cell size and expression of B7 and ICAM-1, and transient release of low levels of immunoglobulin. Complete B cell activation involving the formation of germinal centers and sustained high level RF secretion only occurs if T cell help is provided simultaneously. RF B cells exposed to tolerogen remain competent to secrete RF in vitro if provided with an appropriate antigenic stimulus and T cell help. Consequently, death of these cells is not preceded by anergy. Abortive activation/deletion of B cells by antigen in the absence of T cell-derived survival signals may represent the major mechanism for maintaining peripheral tolerance in B cells expressing higher affinity RF. The lack of anergy, and the potential for reactivation before death, provide a means for maintaining RF production under pathologic circumstances, such as may occur in the inflamed rheumatoid synovium.

Rheumatoid factor production in the joint

Mononuclear cells derived from bone marrow, synovium and peripheral blood of patients with rheumatoid arthritis (RA) were examined for their capacity to produce rheumatoid factor (RF) in order to investigate the origin of circulating RF. The results demonstrate that mononuclear cells derived from bone marrow are able to produce IgG-, IgA- and IgM-RF and that the amounts of RF produced by bone marrow cells are not significantly different from that by dissociated synovial cells. Since circulating immunoglobulins are mainly derived from the bone marrow this observation suggests that also RF circulating in RA patients mainly originates from the bone marrow.

Human monoclonal rheumatoid factors: incidence of cross-reactions with tissue components and correlation with VH gene usage

Human monoclonal antibodies with rheumatoid factor (RF) activity, derived from lymphocytes from the synovial tissue of rheumatoid arthritis (RA) patients and the peripheral blood of healthy individuals were examined for cross-reactivity with tissue and cellular antigens. The majority of IgM RF from RA patients (68%) showed reactivity with at least one component, and were frequently multispecific. A very significantly smaller proportion (28%) of the RF derived from healthy individuals demonstrated reactivities against tissue/cellular antigens (P = 0.004). RF from RA patients most commonly reacted with gastric glands (61%), nuclei (50%) and smooth muscle (50%), whereas RF from healthy donors most commonly reacted with gastric glands (20%), smooth muscle (16%), endothelium (16%) and glomeruli (16%). The most striking difference between the two groups was the reactivity with nuclear components, demonstrated by 50% of the RA RF, but by none of the healthy donor RF. As the two groups of antibodies share the same specificity for IgG Fc, but show differences in variable region segment usage, we investigated the relationship between VH gene usage and tissue/cell cross-reactivity using these antibodies and anti-blood group antibodies. Antibodies using VH3 or VH4 gene segments showed a very significantly greater frequency of tissue/cell reactions than those using VH1 (P = 0.0095 and 0.0004 respectively).

Variable region gene usage of human monoclonal rheumatoid factors derived from healthy donors following immunization

A study was performed to compare the use of immunoglobulin V gene segments by rheumatoid factors (RF) produced in physiological responses following a defined antigenic stimulus, with RF produced in rheumatoid arthritis (RA) and RF produced as monoclonal (M)-components in certain lympho-proliferative diseases. A panel of 46 monoclonal RF was produced, using hybridoma techniques, from healthy individuals following immunization with foreign antigens (mis-matched red blood cells). A panel of previously characterized monoclonal RF from RA synovial tissues was extended to a total of 24 and included in the study. The variable heavy (VH) and variable light (VL) chain gene families used by these RF were determined using idiotypic markers and polymerase chain reaction amplification with VH-specific primers. The frequencies of expression of the various gene families was compared between the two groups, and compared with the published expression frequencies seen amongst M-component RF. The majority (87%) of RF from healthy donors were found with light chains using V gene segments of the V chi 3 family, in conjunction with VH gene segments belonging to the VH1, VH3 and VH4 families. The over-expression of V chi 3, together with the distribution of VH families, demonstrates close similarities with RF found as M-components in lympho-proliferative diseases. In contrast, RF from RA patients showed a predominant use of VH3 gene segments (82%) and an unbiased expression of V chi 3 segments (29% of the chi light chains). These data suggest that RF found as M-components are representative of RF used in normal physiological responses, but have undergone neoplastic or other transformation. RF found in the synovial tissue of RA patients appear to be driven by different mechanisms than RF seen in physiological responses in healthy individuals.

Rheumatoid factor production by mononuclear cells derived from different sites of patients with rheumatoid arthritis

To investigate the origin of circulating rheumatoid factor (RF) and the relation between RF production at different sites in patients with rheumatoid arthritis (RA), mononuclear cells derived from bone marrow, synovium and peripheral blood of patients with RA were examined for the presence of plasma cells and for their capacity to produce RF and other immunoglobulins in vitro. Analysis of culture supernatants for the presence of immunoglobulins demonstrated that cells derived from bone marrow, synovium and peripheral blood were all found to be capable of producing every immunoglobulin and RF isotype investigated. No significant correlations were found between concentrations of immunoglobulin isotypes produced by cells derived from different sites of one individual. Significant correlations were found, however, between concentrations of RF isotypes produced by cells derived from the three sites. These results indicate that the production of RF in the different compartments is not an autonomously regulated process. Mononuclear cells derived from bone marrow were found to be able to produce RF in similar quantities to cells dissociated from synovial tissue. In combination with the fact that circulating immunoglobulins are produced mainly in the bone marrow, this observation suggests that bone marrow is also a major source of circulating RF.

Suppression of anti-erythrocyte autoantibody-producing B cells by a physiological IgG-anti-F(ab')2 antibody and escape from suppression by tumour transformation; a model relevant for the pathogenesis of autoimmune haemolytic anaemia

We showed previously that broadly reactive IgG anti-immunoglobulin autoantibodies produced by rats during the immune response suppress the B cell response. We report here on the effect of a similar human antibody on self-reactive human B cells. IgG anti-F(ab')2 was added to cultures of anti-erythrocyte autoantibody-producing B cells derived from healthy donors. A dose-dependent suppression of the antibody response was obtained (maximum at 1.3 ng IgG/10(6) cells). This effect was competitively inhibited by F(ab')2 gamma. Autoimmune haemolytic anaemia can be caused by chronic monoclonal B cell proliferation. To reproduce this condition in vitro we immortalized B cells with Epstein-Barr virus (EBV) and raised a B cell population with anti-erythrocyte autoantibody activity. These cells were electrically fused with CB-F7 tumour cells and an IgG1 cold-reactive anti-erythrocyte autoantibody-producing B cell line was established. Surprisingly, the tumour cells were not suppressed by IgG anti-F(ab')2. It is known that anti-immunoglobulins selectively suppress antigen-receptor (AgR)-occupied B cells by a Fc gamma-receptor (Fc gamma R)-mediated mechanism. To occupy their AgR, we preincubated the tumour cells with anti-AgR antibody. In spite of this, their susceptibility to suppression was not restored. As shown by rabbit IgG-sensitized ox erythrocyte (EA)-rosetting, this refractoriness was not due to a loss of Fc gamma R. Our experiments delineate a mechanism of peripheral B cell suppression to autoantigens, and show a way of escape from control relevant for the pathogenesis of autoimmune haemolytic anaemia.

Rheumatoid factor and rheumatoid factor isotypes in loiasis with and without accompanying glomerulonephritis

We have studied the distribution of rheumatoid factor isotypes amongst patients with loiasis with and without accompanying glomerulonephritis to determine the possible role of rheumatoid factor antiglobulins in this disease. Our findings indicate an increase in both immunoglobulin (Ig) G and IgM rheumatoid factor isotypes in patients with filariasis alone as well as in patients with accompanying glomerulonephritis. No association with IgA rheumatoid factor was found. The raised IgG and IgM rheumatoid factor levels did not correlate with corresponding IgG and IgM levels.

Restriction mechanisms of B cell regulation by a physiological IgG-anti-immunoglobulin autoantibody

Immunization of LEW rats with strongly histoincompatible BN blood cells induces, in addition to anti-donor antibody, a broadly reactive IgG autoantibody which binds to IgG and IgM molecules (IgG anti-Ig). Minute amounts of affinity purified IgG anti-Ig (0.2 pg/10(6) cells) suppress the antibody production in vitro of antigen receptor (AgR)-stimulated B cells derived from rats of the same strain. The suppressive antibody is also active in the whole serum IgG fraction. Importantly, anti-Ig-induced suppression is governed by restriction mechanisms: only AgR-occupied B cells are affected, the suppression is cell cycle dependent, and maximum suppression is obtained at an optimum IgG concentration. Treatment of rats in vivo with 0.8 mg Ig-anti-Ig (whole IgG fraction) along with allogeneic cells resulted in nearly complete suppression of the anti-donor antibody response. Possible mechanisms of B cell suppression by IgG anti-Ig are crosslinking of AgR with FcR, or cocapping of the two receptors with sterical interaction as a consequence of their separate occupation. Both alternatives lead to the release of an inactivating signal.

Molecular analysis of carbohydrate antigen-induced monoclonal IgM anti-IgG antibodies (rheumatoid factors)

Light and heavy chain variable regions of 11 monoclonal rheumatoid factors (MRF) produced after carbohydrate antigen immunization, and one MRF produced after protein immunization have been sequenced. Most carbohydrate antigen induced MRF utilized light chains that were homologous to light chains of MRF obtained from protein immune or LPS stimulated mice, and MRF derived from the autoimmune MRL/lpr mouse strain. VH gene usage was diverse for carbohydrate antigen induced MRF that bound all four isotypes of IgG, or that bound only the IgG3 isotype. In contrast VH gene use among our panel of MRF that bound the IgG1 isotype appeared restricted. Four of the five IgG1 binders used VH genes that were highly homologous to the VH nucleotide sequence of a gene encoding an NP binding monoclonal antibody. Our study confirms the use of a particular group of light chain genes among murine MRF, confirms that there is diversity in the heavy chain genes utilized among MRF, and suggests that a gene(s) homologous to the VH NP 23 J558 gene may be preferentially associated with murine MRF specificity for the IgG1 isotype.

Regulation of antibody production mediated by Fc gamma receptors, IgG binding factors, and IgG Fc-binding autoantibodies

Fc receptors (FcRs) are immunoglobulin-binding structures that enable antibodies to perform a variety of functions by forming connections between specific recognition and effector cells. Besides eliciting cytotoxicity, inducing secretion of mediators and endocytosis of opsonized particles, FcRs are involved in the regulation of antibody production, both as integral membrane proteins and as soluble molecules released from the cell surface. Most FcRs belong to the same family of proteins as their ligands (immunoglobulin superfamily). This review contains recent data obtained by use of monoclonal antibodies and cloning studies on FcRs and FcR-like molecules. The importance of fine specificity of receptor binding site(s)--that of the conformation of FcRs and their ligands in triggering signaling mechanisms--is analyzed. The regulatory function of membrane-bound and -released FcRs; the correlation between cell cycle, FcR expression, and release; as well as the possible mechanisms of these phenomena are discussed.

Rheumatoid factor (RF) distribution in periodontal disease

This study investigated the occurrence of an autoantibody, IgM rheumatoid factor, that may result from the chronic inflammation noted in periodontal disease and rheumatoid arthritis. In order to detect IgM-RF, a biotin-avidin ELISA was developed. This assay was found to be sensitive and accurate by testing a rheumatoid arthritis population. The characteristics of this rheumatoid arthritis group were further determined, such that the total serum immunoglobulin concentrations were slightly elevated although within the normal range for IgM, IgG, and IgA; IgG antibody levels were elevated against oral microorganisms of the genus Capnocytophaga, while elevated IgM antibody levels were noted to Bacteroides species. In a population of 260 subjects of which 171 were periodontal disease patients, 16 of 171 (9.4%) were seropositive for IgM-RF, of which the predominant disease types were advanced destructive periodontitis and adult periodontitis. For comparison, a random population of seronegative periodontal disease patients was constructed that was matched for sex and approximate age to the seropositive group. The total immunoglobulin levels of the two groups were not significantly different and the means of both were slightly lower than the rheumatoid arthritis group. When the antibody profiles of the two periodontal disease populations were compared it became evident that the RF-positive group showed IgM and IgG antibody that was significantly elevated to Capnocytophaga species and F. nucleatum. Therefore, the chronic inflammation associated with periodontitis appears to increase significantly the formation of IgM-RF; however, there does appear to be a relationship between IgM-RF and elevated antibody to selected oral microorganisms.

In situ studies of the primary immune response to (4-hydroxy-3-nitrophenyl)acetyl. I. The architecture and dynamics of responding cell populations

After primary immunization with an immunogenic conjugate of (4-hydroxy-3-nitrophenyl)acetyl, two anatomically and phenotypically distinct populations of antibody-forming cells arise in the spleen. As early as 2 d after immunization, foci of antigen-binding B cells are observed along the periphery of the periarteriolar lymphoid sheaths. These foci expand, occupying as much as 1% of the splenic volume by day 8 of the response. Later, foci grow smaller and are virtually absent from the spleen by day 14. A second responding population, germinal center B cells, appear on day 8-10 and persist at least until day 16 post-immunization. Individual foci and germinal centers represent discrete pauciclonal populations that apparently undergo somatic evolution in the course of the primary response. We suggest that foci may represent regions of predominantly interclonal competition for antigen among unmutated B cells, while germinal centers are sites of intraclonal clonal competition between mutated sister lymphocytes.

Isolation and characterization of IgG2a-reactive autoantibodies from influenza virus-infected BALB/c mice

Repeated influenza virus infection induces the production of dominantly IgG2a-type virus-specific antibodies as well as the appearance of IgG2a-reactive autoantibodies in BALB/c mice characterized by low spontaneous rheumatoid factor-type autoantibody production. IgG2a-reactive autoantibody-producing hybridomas could be isolated from the spleen of influenza virus-infected BALB/c mice. The mAb produced by these clones represent not only IgM but also IgG and IgA isotypes and show strong isotype or isoallotype specificity. The common functional property of these autoantibodies is their preferential- and high-affinity binding to complexed, solid-phase-bound or heat-aggregated IgG2a when compared to native soluble or cell-bound IgG2a. The mechanism of induction and the possible biological function of these autoantibodies are discussed in the light of their fine specificity and functional properties.

In vivo manipulation of IgG2a production by isotype-specific autoantibodies

Repeated intranasal infection of Balb/c mice with A/PR/8 influenza virus induced an intense antiviral IgG response dominated by the IgG2a subclass, and accompanied by the appearance of IgG2a reactive autoantibodies. Cells producing IgG2a reactive autoantibodies could then be cloned as hybridomas from the virus infected animals. Monoclonal antibodies produced by selected hybridomas U28, Z26 and Z41 produced IgM-type antibodies with strong specificity for the IgG2a isotype bearing "a" allotypic determinants on the Fc region. These IgG2a specific autoantibodies showed highly preferred binding to solid phase bound or aggregated IgG2a, compared to soluble native IgG2a. Based on these characteristics they were classified as mono-reactive rheumatoid factor (RF)-like autoantibodies. Passive administration of IgM type IgG2a-specific autoantibodies to influenza virus infected animals resulted in a long-term reduction in the secondary antiviral response. This could be demonstrated by decreased virus neutralizing activity of the serum and diminished level of IgG2a-type anti-viral antibodies. A similar effect was observed in Balb/c mice contact sensitized with oxazolone: passive administration of RF-like antibodies resulted in reduced IgG2a response to oxazolone while the level of antibodies belonging to other isotypes was not influenced. These results suggest an isotype-specific regulatory function of these RF-like autoantibodies presumably acting via antigen-antibody complexes.

Frequency and phenotypic feature of autoantibody-producing cell precursors in the preclinical stage of murine lupus

The present study addresses the question of whether there is a difference in the frequencies of autoantibody-producing B-cell precursors in healthy compared with lupus-prone mouse strains. Spleen mononuclear cells (MNC) from 4-week-old (i.e. at the preclinical stage of lupus) mice were activated in vitro for 3 and 6 days with lipopolysaccharides (LPS) and the numbers of IgG, IgA and IgM autoantibody-producing cells were analysed by the ELISPOT assay. The results indicate a high frequency of IgM autoantibody-secreting cells after both 3 and 6 days in vitro stimulation. In spite of high frequencies of IgG-producing cells appearing late during the course of LPS stimulation, no IgG or IgA autoantibody producing cells were detected. No significant differences in the autoantibody repertoire were noted between healthy and lupus-prone mice, indicating that independent of the genetic background the immune system has the capacity to react with autoantibody production. Phenotypic analysis of LPS-induced, IgM-secreting B cells showed clearly that the majority of them were surface IgM+, CD5+ but Thy-1-.

In vitro IgG rheumatoid factor production by CD5-negative murine B cells in response to immune complexes of lipopolysaccharide

We studied the in vitro production of rheumatoid factor (RF) by spleen cells of normal adult mice. IgG RF cross-reactive with rabbit IgG was produced in response to immune complexes of TNP-lipopolysaccharide (LPS) with murine IgG anti-TNP antibody in an Fc-specific manner, but not to a mixture of IgG and LPS. Antibody-uncomplexed LPS induced little IgG RF production, but suppressed the subsequent IgG RF response to antibody-complexed LPS, whereas IgM RF was induced by either LPS or antibody-complexed LPS. The IgG RF production followed as rapid a time course as IgM RF production; the rate of IgG RF production reached its maximum soon after a lag period of 1 day and declined after 5 days. Treatment of splenic B cells from BALB/c mice with anti-Ly-1.2 antibody and rabbit complement resulted in a selective reduction of IgM RF production by 90%, with little effect of IgG RF production. These results suggest that IgG RF is derived primarily from CD5- memory B cells which have been developed in normal mice by an unknown mechanism. Unlike the CD5+ precursor cells for IgM RF, these memory cells are unresponsive to polyclonal stimulation by LPS but are activated by simultaneous stimulation by aggregated Fc epitopes and the mitogenic stimulus from LPS.

Monoclonal IgM rheumatoid factor-like anti-globulins enhance the inhibitory effects of Plasmodium falciparum-specific monoclonal antibodies in vitro

Monoclonal IgM rheumatoid factor-like anti-globulins were produced by in vitro stimulation of naive BALB/c spleen cells with lipopolysaccharide, and by hyperimmunization of mice with merozoites of Plasmodium falciparum, followed by fusion of the spleen cells to mouse myelomas. In vitro, these anti-globulins augmented the inhibitory effects of P. falciparum-specific polyclonal mouse sera and monoclonal IgG1 and IgG2b antibodies by binding to Fc fragments of IgG molecules attached to blood-stage parasites. In some instances, the presence of anti-globulins correlated with an increase in the number of schizonts which failed to disperse merozoites. In other cases, parasitaemia remained low in the absence of the schizont inhibition phenomenon, suggesting that anti-globulins contribute to host cell protection not only by agglutinating merozoites, but also by increasing the density of the antibody coat surrounding the parasites, thus interfering with parasite receptor-erythrocyte ligand interactions. The anti-globulins were not inhibitory when added to parasite cultures containing IgG not specific for P. falciparum. These results may help explain the function of IgM anti-globulins found at elevated serum levels in some patients with malaria or other chronic infectious diseases.

In vitro secretion of human IgM rheumatoid factor. Evidence for distinct rheumatoid factor populations in health and disease

The production of antibodies that react with the Fc fragment of IgG, i.e., rheumatoid factors (RF), is now regarded as a normal host immune response. It is not clear, however, if such putative physiologic RF are different from their counterparts which characterize pathologic states like rheumatoid arthritis (RA). Using Staphylococcus aureus Cowan I as an in vitro stimulant of RF production, we now report that the IgM-RF secreted by blood mononuclear cells obtained from healthy newborn infants and healthy adults can be distinguished not only from classic monoclonal RF and polyclonal RA serum RF, but also from the RF secreted by blood mononuclear cells obtained from RA patients. Whereas the Fc-binding activity of all RF secreted in vitro was easily inhibited by aggregated human IgG, only the RF produced by the normal umbilical cord cells and the normal adult cells were inhibited by monomeric Fc(IgG). The normal RF were also selectively inhibited by monomeric rabbit and guinea pig (Fc(IgG). The RF secreted by umbilical cord blood cells utilized lambda and kappa light chains, with a disproportionate use of lambda light chains relative to the total IgM secreted. Together, these data provide evidence for distinct subsets of RF in health and in disease.

Evidence that the Fc region of autologous rabbit IgG isolated before and after hyperimmunization is structurally different: recognition by rheumatoid factor and monoclonal antibodies

Autologous hyperimmune (HI) and pre-inoculation (PI) rabbit Fc gamma populations were found to be conformationally different by spectroscopic measurements, and antigenically different by measurements which examined rheumatoid factor (RF) and monoclonal antibody (MoAb) binding specificity for both populations in ELISA. Circular dichroism spectra of HI rabbit Fc gamma (prepared from animals after hyperimmunization with streptococcal vaccine) were both qualitatively and quantitatively different, particularly in the 225-228 nm range, in comparison to both homologous normal and autologous PI Fc gamma. Binding studies in ELISA showed that affinity constants obtained for reactions of both rabbit RF and various murine MoAb with HI IgG and Fc were approximately 10-fold higher relative to those observed for PI IgG and Fc. Enzymatic deglycosylation of HI and PI Fc gamma led to elimination of CD spectral differences. Further, association constants obtained for RF and MoAb reactions with deglycosylated (sialic acid and galactose removed) PI Fc gamma were equivalent to those obtained in the presence of untreated HI Fc gamma. Together, these results suggest the complex oligosaccharide structure of rabbit IgG may play a significant role in the expression of Fc gamma determinants, and alteration of this structure under hyperimmune or other conditions may be related to induction of an RF response.

Human IgG anti-F(ab')2 antibodies possess rheumatoid factor activity

Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.

Streptococcus mutans and the problem of heart cross-reactivity

Investigations of immune responses to Streptococcus mutans have fostered consideration of vaccination as a possible preventive measure against dental caries. However, the finding that hyperimmune rabbit antisera to S. mutans sometimes give immunofluorescent reactions on human heart raised concerns over safety, especially as most individuals display circulating antibodies to this common oral organism. Recent progress in elucidating the molecular mechanisms of the well-established immunological cross-reactivity between group A streptococci and human heart tissue and the structure of S. mutans antigens permits a re-evaluation of this problem. This review examines the evidence for heart cross-reactivity induced by S. mutans in relation to studies on group A streptococci and current understanding of autoimmunity. Although the mechanisms involved in this phenomenon need further clarification, it now appears that it cannot be ascribed to antigenic similarity between heart tissue and a high-molecular-weight surface protein antigen of S. mutans.

IgG isotype and isotype specificity of murine monoclonal IgG rheumatoid factors

Immune complexes of lipopolysaccharide (LPS) with homologous IgG antibody induces rheumatoid factor (RF) predominantly of the IgG class in normal mice, while LPS alone induces mostly IgM RF directed to homologous IgG1. In this study, IgG monoclonal RFs (mRF) were prepared from hybridomas derived from spleen cells of BALB/c mice which were immunized with complexes of TNP-LPS with anti-TNP mouse IgG and their specificity to mouse IgG subclasses was assessed by analysing dissociation kinetics of the ligands due to RF-specific and non-specific interactions. Of the 19 IgG mRFs (11 IgG1, five IgG2a, one IgG2b and two IgG3 types) tested, 14 were directed to either IgG3 or IgG2b or both, while only one exhibited a significant binding capacity to IgG1. Other mRFs, although reactive to rabbit IgG, exhibited little homophilic activity. None of these mRFs reacted strongly with their own isotypes. The results suggest that the IgG RF producing cells are not direct progenies of the IgG1-directed IgM RF-producing cells but may have developed via a rigorous selection process to eliminate clones that produce self-reactive RF.

Rheumatoid factor induction in the mouse: sex differences and the effect of the sex steroids

Female CBA mice produced a significantly higher plasma rheumatoid factor (RF) response to Salmonella typhosa lipopolysaccharide than did male mice. The peak level in females was observed on day 5-6 after injection and in males on day 7-8. Elevated RF levels continued to be detected more than 30 days later. A second injection of LPS, 38 days after the first, to assess the secondary response, had no more than an additive effect on plasma RF concentration, although the day of peak response was earlier by two days in both sexes. Administration of oestradiol-17 beta by Silastic implant brought forward the day of peak response by two days in both sexes although it reduced its amplitude considerably. Testosterone had little effect on the peak concentrations achieved in both sexes, but did produce a slower decay in plasma RF level. This investigation indicates that the sex hormones can influence the response to LPS, a polyclonal B cell activator. This may have implications for the sex differences seen in autoimmune diseases.

I-E-linked control of spontaneous rheumatoid factor production in normal mice

The concentration of serum IgM molecules binding to IgG2a (rheumatoid factor [RF]) in solid phase assays is 10-100-fold higher in normal, unmanipulated C3H/HeJ (H-2k) than in C57BL/6 (H-2b) mice. Analysis of MHC-congenic mice with the prototype strains show that C3H SW (H-2b) are low, and B6.H-2k are high RF expressor strains, respectively. Furthermore, segregation of RF phenotypes in progenies from backcrosses to C3H/HeJ of (C3H/HeJ x C57BL/6)F1 hybrid mice shows MHC- and IgH-linked controls. RF phenotypes also segregate as if they are MHC linked in crosses between H-2-congenic strains (C3H/HeJ and C3H.SW). The study of intra-H-2 (k/b and k/s) recombinant mice suggested that RF phenotype control is linked to the I-E region. This was confirmed by the typing of C57BL/6 mice expressing a transgenic E alpha chain, and thus, I-E+, which, in contrast to nontransgenic littermates, are high expressors of RF.

Rheumatoid factor autoantibody-binding site: a molecular analysis using monoclonal antibodies with dual anti-TNP and anti-IgG activities

Two out of five murine IgG3 anti-trinitrophenyl (TNP) monoclonal antibodies (mAb) obtained either by immunization with TNP-keyhole limpet hemocyanin (KLH) (CB1, CB5, CB6 and 4H10) or with dinitrophenyl-lipopolysaccharide (9A6), exhibited anti-IgG rheumatoid factor (RF) activity (CB6 and 4H10). The anti-IgG activity of these two anti-TNP RF was specifically inhibited by murine IgG as well as by the hapten TNP. In order to identify the structural basis for the anti-IgG activity, the nucleotide sequences encoding the VH and VL regions were determined. By comparing the V regions of the non-RF and RF anti-TNP mAb, it was found that one anti-TNP RF antibody, CB6, shares virtually identical VL and VH regions with two anti-TNP antibodies, CB1 and CB5, but markedly differs from these in the D region. Furthermore, the light chain framework region 2 (FR2) and FR3 of non-RF mAb, CB1, CB5 and 9A6, have amino acid sequences almost identical to those claimed for anti-IgG1 RF activity (Shlomchik et al., J. Exp. Med. 1986. 164: 407). Our findings suggest, at least in the case of CB6 mAb, the involvement of CDR, but not light chain FR residues, in IgG binding.

Rheumatoid factor blocks regulatory Fc signals

Immunosuppressed cultures of murine spleen cells, partly deprived of T cells and antigen-stimulated, can be reconstituted to near full activity in their antibody-forming cell response with murine rheumatoid factors (RF). The dose of RF required for recovery of 50% of the reconstitutable immune response was 10-100 ng and reconstitution was blocked by intact murine IgG added to the cultures. IgG subclass specificity of RF was demonstrated; RF specific for IgG2a was more potent than RF specific for IgG1 in reconstituting the response. Synergy was observed between RF added at culture initiation and late-acting B-cell differentiation factors. The greater the degree of T-cell deprivation, the more stringent the conditions needed for reconstitution. Suitable conditions for reconstitution with profound T-cell depletion included the limited reconstitution by specific RF, the synergistic action of RF with late-acting T-cell-replacing supernatants, and multiple additions of a number of RFs to the cultures on Days 0, 1, and 2. RF was also shown to block Fc-dependent immunosuppression by added antigen-antibody complexes. These results are interpreted as favoring the hypothesis put forward previously that the normal production of RF acts to reduce T-cell dependency by preventing negative Fc signal transmission by immune complexes on the B-cell surface. Abnormal production of RF may be a primary destabilizer of the immune responses leading to autoimmunity.

Activation of clones producing self-reactive antibodies by foreign antigen and antiidiotype antibody carrying the internal image of the antigen

Because we found in previous work that a high fraction of antibodies exhibiting various specificities bound to glutamic acid 50-tyrosine50 homopolymer (GT) and expressed pGAT cross-reactive idiotype (IdX), we studied the activation of clones producing multireactive antibodies in 1-mo-old MRL/lpr and C3H/HeJ mice bearing VHJ haplotype. The activation of such clones was studied after mice were immunized with GT in CFA, HP20 (an anti-Id MAb carrying the internal image of GT in the D region), and a synthetic peptide corresponding to the D segment of HP20. Our results indicate that immunized mice produced both GT- and self-reactive antibodies. Study of the immunochemical properties of MAb showed that they exhibit multispecific properties and bind with similar-affinity constants to GT or self-antigens such as DNA, Smith antigen (Sm), and IgG2a. An important fraction of antibodies obtained from MRL/lpr mice immunized with HP20 expressed pGAT IdX and some of these antibodies share IdX expressed on anti-DNA, Sm, and rheumatoid factor (RFs) antibodies. The hybridomas producing multispecific autoantibodies use heavy-chain- (VH) and light-chain-variable region (VK) genes from various V gene families, suggesting that they do not derive from the pool of GAT precursors. Sequencing of VH and VK genes of two antibodies show that they can use closely related VHJ558, unmutated VK1, or different VK genes than those used by anti-GT antibodies. Our data demonstrate that clones producing antibodies binding to GT and self-antigens with similar-affinity constants can be activated by foreign or anti-Id antibodies carrying the internal image of the antigen or even by a synthetic peptide corresponding to the D segment of anti-Id antibodies.

Rheumatoid factor and Fc signaling: a tale of two Cinderellas

Signaling to lymphocytes depends not only upon the interaction of receptors with specific antigen, but also upon antigen nonspecific receptors which receive input from two classes of molecules, immunologically specific end products and lymphokines. These represent the central elements in the physiologic stimulation of immune responses to both self and foreign antigens. This review is dedicated primarily to describing the function of physiologically active receptors for end product which are central to end product feedback in normal immune responses. The emergence of autoimmunity as a pathologic process resultant from a defective end product signaling mechanism is described.

Local production of IgA- and IgM-rheumatoid factors in adult periodontal disease

The enzyme-linked immunospot assay was used to enumerate both the number and the frequency of spontaneous IgG, IgA, and IgM immunoglobulin-secreting cells and IgA- and IgM-rheumatoid factor (RF)-producing cells present in the gingivae and peripheral blood of adult periodontitis patients. Cells from 29 patients were incubated on plates coated with human IgG, Fc, or F(ab')2 fragments and on plates coated with class-specific anti-human antibodies and secreted antibodies were subsequently visualized by means of an immunoenzymatic procedure. The data indicate that (1) IgA-RF- and IgM-RF-secreting cells are frequently present in the gingiva of adult periodontitis patients; (2) production of RF in gingivae of adult periodontitis patients occurs in the absence of demonstrable RF production by simultaneously obtained peripheral blood mononuclear cells, suggesting that local autoimmune reactions may occur in this disease; and (3) lack of correlation between IgA-RF and IgM-RF production in diseased gingiva suggests that the two RF isotypes are regulated independently of each other.