Characterization of multireactive autoantibodies and identification of Leu-1+ B lymphocytes as cells making antibodies binding multiple self and exogenous molecules

Targeted Therapies for Autoimmune Bullous Diseases: Current Status

Autoimmune bullous skin disorders are rare but meaningful chronic inflammatory diseases, many of which had a poor or devastating prognosis prior to the advent of immunosuppressive drugs such as systemic corticosteroids, which down-regulate the immune pathogenesis in these disorders. Glucocorticoids and adjuvant immunosuppressive drugs have been of major benefit for the fast control of most of these disorders, but their long-term use is limited by major side effects such as blood cytopenia, osteoporosis, diabetes mellitus, hypertension, and gastrointestinal ulcers. In recent years, major efforts were made to identify key elements in the pathogenesis of autoimmune bullous disorders, leading to the identification of their autoantigens, which are mainly located in desmosomes (pemphigus) and the basement membrane zone (pemphigoids). In the majority of cases, immunoglobulin G, and to a lesser extent, immunoglobulin A autoantibodies directed against distinct cutaneous adhesion molecules are directly responsible for the loss of cell-cell and cell-basement membrane adhesion, which is clinically related to the formation of blisters and/or erosions of the skin and mucous membranes. We describe and discuss novel therapeutic strategies that directly interfere with the production and regulation of pathogenic autoantibodies (rituximab), their catabolism (intravenous immunoglobulins), and their presence in the circulation and extravascular tissues such as the skin (immunoadsorption), leading to a significant amelioration of disease. Moreover, we show that these novel therapies have pleiotropic effects on various proinflammatory cells and cytokines. Recent studies in bullous pemphigoid suggest that targeting of immunoglobulin E autoantibodies (omalizumab) may be also beneficial. In summary, the introduction of targeted therapies in pemphigus and pemphigoid holds major promise because of the high efficacy and fewer side effects compared with conventional global immunosuppressive therapy.

B cell TLRs and induction of immunoglobulin class-switch DNA recombination

Toll-like receptors (TLRs) are a family of conserved pattern recognition receptors (PRRs). Engagement of B cell TLRs by microbe-associated molecular patterns (MAMPs) induces T-independent (TI) antibody responses and plays an important role in the early stages of T-dependent (TD) antibody responses before specific T cell help becomes available. The role of B cell TLRs in the antibody response is magnified by the synergy of B cell receptor (BCR) crosslinking and TLR engagement in inducing immunoglobulin (Ig) class switch DNA recombination (CSR), which crucially diversifies the antibody biological effector functions. Dual BCR/TLR engagement induces CSR to all Ig isotypes, as directed by cytokines, while TLR engagement alone induces marginal CSR. Integration of BCR and TLR signaling results in activation of the canonical and non-canonical NF-κB pathways, induction of activation-induced cytidine deaminase (AID) and germline transcription of IgH switch (S) regions. A critical role of B cell TLRs in CSR and the antibody response is emphasized by the emergence of several TLR ligands as integral components of vaccines that greatly boost humoral immunity in a B cell-intrinsic fashion.

Specificity mapping of human anti-T cell receptor monoclonal natural antibodies: defining the properties of epitope recognition promiscuity

The classical concept of antibody binding is defined as an exclusive and high-affinity interaction with one epitope. The emerging reality about antibody combing sites, however, is that some can bind unrelated determinants. The studies presented here define this quality as epitope recognition promiscuity by analyzing the capacity of monoclonal human autoantibodies to bind sets of overlapping peptides duplicating the complete structures of T cell receptor (TCR) alpha and beta chains and immunoglobulin lambda chain. We assessed the binding of these monoclonal antibodies (mAbs) to a set of homologous peptides corresponding to the CDR1 segments of human Vbeta gene products, a major epitope used in the selection of the antibodies. We present data on the binding characteristics of four human mAbs selected for the ability to bind TCR epitopes. These mAbs are IgM molecules with VH and VL sequences in germline configuration, but have diverse VH CDR3 regions. These studies aim to characterize the property of epitope promiscuity and show that the relationship between the binding site and its epitope is a complex interaction and unpredictable from antigen sequence alone. Our results support the conclusion that epitope recognition promiscuity is a genuine feature of antibody and TCR recognition.

Natural antibodies and the host immune responses to xenografts

Natural antibodies are present in the serum of individuals in the absence of known antigenic stimulation. These antibodies are primarily IgM, polyreactive, and encoded by immunoglobulin V genes in germline configuration. Natural antibodies are produced by B-1 lymphocytes, cells that form the primary cell of the fetal and newborn B cell repertoire and may represent the basic foundation upon which the adult repertoire of B cell antibodies is based. Natural antibodies react with a variety of endogenous and exogenous antigens, including xenoantigens expressed by tissues between unrelated species. These antibodies are capable of causing the immediate rejection of grafts exchanged across species barriers. One of the central issues related to our understanding of the immunopathologic mechanisms responsible for rejection of xenografts is whether pre-formed natural antibodies and new antibodies induced following xenotransplantation are produced by the same pathways of B cell antibody production. We have established in studies conducted in rodents and humans that the initial phases of antibody production xenogeneic tissues involves the use of a restricted population of Ig germline genes to encode xenoantibody binding. As the humoral xenoantibody response matures, the same closely-related groups of Ig V genes are used to encode antibody binding and there is evidence for an isotype switch to IgG antibody production and the appearance of somatic mutations consistent with antigen-driven affinity maturation. Our findings in both rodent and human studies form the basis for our proposal that the xenograft response reflects the use of B cell natural antibody repertoires originally intended to provide protection against infection. The host humoral response is inadvertently recruited to mount antibody responses against foreign grafts because they display carbohydrate antigens that are shared by common environmental microbes. This model of xenoantibody responses is being tested in our laboratory through the analysis of the binding of xenoantibodies in their original non-mutated configuration, and the examination of the effect of specific point mutations and gene shuffling have on xenoantibody binding activity. Establishment of the relationships between Ig structural changes and subsequent changes in binding affinity should provide important insights into the role that, natural antibodies and the cells that produce them play in the evolution of the host's humoral responses to xenografts.

Depletion of peritoneal CD5+ B cells has no effect on the course of Leishmania major infection in susceptible and resistant mice

The mouse peritoneal cavity contains a unique self-renewing population of B cells (B-1) derived from fetal liver precursors and mainly producing polyreactive antibodies. Since B-1 cells are a potential source of IL-10, it has been suggested that these cells may contribute to the susceptibility of BALB/c mice to Leishmania major infection by skewing the T helper cell network towards a Th2 phenotype. Accordingly, L. major infection of B cell-defective BALB/c Xid mice (lacking B-1 cells) induces less severe disease compared with controls. However, in addition to the lack of B-1 cells, the Xid immune deficiency is characterized by high endogenous interferon-gamma (IFN-gamma) production. In the present study, the role of B-1 cells during L. major infection was investigated in mice experimentally depleted of peritoneal B-1 cells. Six weeks old C57Bl/6 and BALB/c mice were lethally irradiated and reconstituted with autologous bone marrow which allows systemic depletion of B-1 cells. Untreated BALB/c, C57Bl/6 as well as BALB/c Xid mice were used as controls. After reconstitution, mice were injected with L. major amastigotes and progression was followed using clinical, parasitological and immunological criteria. As previously reported, BALB/c Xid mice showed a significant reduction in disease progression. In contrast, despite the dramatic reduction of B-1 cells, B-1-depleted BALB/c mice showed similar or even worse disease progression compared with control BALB/c mice. No differences were found between B-1-depleted or control C57Bl/6 mice. Our data suggest that the B-1 cells do not contribute to the susceptibility of BALB/c mice to L. major infection.

Cellular Basis of B Cell Clonal Populations in Old Mice

Previous studies from this laboratory have shown that >85% of old mice have stable B cell clonal populations detectable by Ig heavy chain complementary-determining region 3 mRNA size analysis and confirmed by sequence analysis. B cells from the same clone are frequently detected in several lymphoid compartments of the same mouse. We now report the phenotype of all ten stable B cell clonal populations detected in five 20-month-old C57BL/6 mice. These clonal B cells appear to develop in the periphery and nine of the ten B cell clonal populations expressed the CD5 cell surface marker. Stable B cell expansions may be dominated by cells at two stages of differentiation. Some B cell populations were detected with DNA as well as RNA and represent large clonal populations of B cells, detectable in several lymphoid compartments. These populations are found predominantly in B cell populations expressing CD45R/B220 and the mRNA coding for the membrane-bound form of the μ Ig heavy chain, which suggests a predominance of B lymphocytes in these populations. In other cases, smaller clonal populations were detected only in splenic RNA samples. These clonal populations were found predominantly among CD45R/B220− B cells and did not express the membrane-bound form of the μ Ig heavy chain. We offer the hypothesis that the B cell clonal populations present in old mice may be precursors of the two types of B cell neoplasms which are dominated by CD5+ B cells (B cell chronic lymphocytic leukemia) or plasma cells (multiple myeloma).

Pooled Normal Human Polyspecific IgM Contains Neutralizing Anti-Idiotypes to IgG Autoantibodies of Autoimmune Patients and Protects From Experimental Autoimmune Disease

Normal human serum contains IgM antibodies that regulate the natural autoantibody activity of IgG in autologous serum. In the present study, we show that pooled normal human IgM (IVIgM) purified from plasma of more than 2,500 healthy donors and processed in a similar fashion to that of therapeutic preparations of pooled normal human IgG (IVIg) suppresses activity of IgG autoantibodies purified from the serum of patients with autoimmune diseases in vitro. The inhibitory effect of IVIgM was greater or equivalent to that of IVIg on a molar basis. We show that IVIgM contains anti-idiotypic antibodies directed against idiotypic determinants of autoantibodies, in particular by showing that Sepharose-bound IVIgM selectively retained F(ab′)2 fragments of IgG autoantibodies. The infusion of (Lewis × Brown-Norway) F1 rats with IVIgM protected the animals against experimental autoimmune uveitis induced by immunization with the soluble retinal S antigen, as evidenced by clinical scoring and histopathological analysis. The present findings provide a rationale for considering pooled IgM for immunomodulation of autoimmune disease.

Natural polyreactive secretory immunoglobulin A autoantibodies as a possible barrier to infection in humans

Secretory immunoglobulin A (S-IgA) was investigated in human secretions for the presence of natural antibodies (Abs) acting as the first "immune barrier" to infection before induction or boosting of specific responses. These molecules could be the secretory counterpart of the natural Abs in serum that were previously shown by our laboratory to be polyreactive to autoantigens. Significant levels of S-IgA Abs to human actin, myosin, tubulin, and spectrin were detected in 10 saliva and 8 colostrum samples from normal subjects. Computer-assisted analysis of immunoblots of extracts from human muscles showed these Abs to react with a large number of autoantigens. Their polyreactivity was confirmed by cross-inhibition and by immunoblotting studies of affinity-purified natural Abs, assayed against a large variety of surface or secreted antigens from Streptococcus pyogenes. The thiocyanate elution method showed that functional affinities of some natural Abs can be of the same order of magnitude as those of tetanus vaccine antitoxins. Moreover, nonimmune binding of these natural Abs to the gut protein Fv (Fv-fragment binding protein) can enhance their effector functions. This demonstrates that human secretions contain polyreactive auto-Abs which can also react with pathogens. These secretory Abs of "skeleton key" specificities are possibly produced by a primordial B-1-cell-associated immune system and can be involved in a plurispecific mucosal protection against pathogens, irrespective of the conventional immune response.

B cell development in mice

The development and establishment of the B Cell Repertoire is the net result of both genetic and environmental forces. The primary event at the genetic level is Ig gene rearrangement resulting in numerous possible combination of genes which can be further modified by somatic events such as N segment addition and somatic mutation. Environmental forces in the form of self and exogenous Ags also shape the repertoire by positively or negatively selecting B cells according to the specificity of their Ig receptors. These are dynamic processes beginning with the earliest expression of immunoglobulins in fetal life and continuing throughout life. In this review we discuss the genetic and selective mechanisms responsible for differences in the early immune system compared to that of the adult.

Normal human cord blood B cells can produce high affinity IgG antibodies to dsDNA that are recognized by cord blood-derived anti-idiotypic antibodies

It is possible to identify, in Epstein-Barr virus-transformed normal human cord blood B cell populations, cells present at a low frequency that produce IgG antibodies specific for dsDNA. By cloning out these B cells as immortalized monoclonal cell lines, it could be shown that the antibodies were the products of CD5 positive B cells. Two monoclonal anti-dsDNA antibodies were derived from cell lines T52 and A7 and these were further characterized as anionic (pI approximately 6.4) IgG4 kappa antibodies that bound with affinities of 7.18 x 10(9) l/mol and 3.28 x 10(9) l/mol, respectively, to dsDNA but did not bind to ssDNA. These affinities were similar to those of polyclonal IgG anti-dsDNA antibodies from lupus patients, which ranged from 1 x 10(9) -8.9 x 10(10) l/mol. Both T52 and A7 monoclonal anti-dsDNA antibodies were recognized by cord blood-derived IgM antibodies. These IgM antibodies were not rheumatoid factors but bound to the F(ab')2 of A7 and T52 while failing to recognize T50, which is an autologous IgG4 kappa monoclonal antibody without specificity for dsDNA. A cloned B cell line A24 generated from the same cord blood sample as A7 produced an IgM monoclonal antibody that bound to the heavy chains of T52 and A7, but not T50 on Western blot and inhibited the binding of these antibodies to dsDNA. A7 and T52 competitively inhibited each other in their binding to the anti-idiotype A24, and A24 inhibited the binding to dsDNA of some polyclonal IgG anti-dsDNA antibodies purified from sera of lupus patients. The level of inhibition of binding of these antibodies to dsDNA was directly proportional to the levels of expression of the idiotype recognized by A24 on these antibodies. The normal human cord blood, therefore, may contain cells that form an idiotype/anti-idiotype network in which the idiotype is expressed on IgG antibodies with specificity for dsDNA and the anti-idiotype is an IgM antibody that binds to a heavy chain idiotope in such a way as to interfere with its interaction with dsDNA. The presence of a similar idiotype on some polyclonal anti-dsDNA antibodies in lupus that are similarly inhibitable by the cord blood-derived anti-idiotype raises the possibility that this network may persist in later life and perhaps become dysfunctional in systemic lupus erythematosus.

The CD5+ B cells and myasthenia gravis

A high frequency of CD5+ B lymphocytes in the peripheral blood of patients with myasthenia gravis (MG) has been reported recently. These results seem to indicate an attractive linkage between CD5+ B lymphocytes and autoantibodies against Acetylcholine receptor in MG. We examined the frequency of CD5+ B cells in 20 patients with MG and 21 normal healthy controls by two-color flow cytometry. However, there were no significant differences in the percentages of CD5+ B lymphocytes between the two groups. We also examined the frequency of CD5+ B lymphocytes in the resected thymus of patients. The frequency of CD5+ B lymphocytes in the thymus was low and similar pattern to that in the peripheral blood. We checked the antibody (Ab) production against the human acetylcholine receptor in either CD5+ B or CD5- B lymphocytes using B lymphoblastoid cell line generated from the lymphocytes of 11 patients with anti-AChR Abs in the sera. Abs against the AChR in the human were mostly produced by CD5- B, not CD5+ B lymphocytes. The anti-AChR Abs (IgG) production of CD5+ B cells and CD5- B cells (mean +/- SD) were 6.8 +/- 2.4 fmol/ml and 18.5 +/- 17.6 fmol/ml, respectively. These results suggest that in MG, the frequencies of the CD5+ B lymphocytes in PBL may be genetic background and that there may be no strong linages between AChR Ab production and CD5+ B lymphocytes.

Anti-islet cell and anti-insulin antibody production by CD5+ and CD5- B lymphocytes in IDDM

Although CD5 + B lymphocytes are mostly committed to the production of polyreactive natural autoantibodies, CD5 + B lymphocytes committed to the production of somatically mutated and monoreactive high-affinity IgM autoantibodies have been also shown. Increased proportions of CD5 + B lymphocytes in some autoimmune diseases, including insulin-dependent diabetes mellitus (IDDM), have been noticed. The present study was undertaken to analyse the differences between CD5 + and CD5- B lymphocyte subsets for production of IDDM-related autoantibodies, i.e. anti-human insulin antibodies (IA) and anti-human islet cell antibodies (ICA). For this purpose, Epstein-Barr Virus (EBV)-transformation of FACS cell-sorted CD5 + and CD5- B lymphocytes and unfractionated enriched B lymphocytes from nine IDDM patients treated exclusively with recombinant human insulin, and from four healthy control subjects was performed; a mean of 102-216 microcultures with a mean of 1,000-2,333 cells/microculture for each B-lymphocyte fraction and individual was established. Data show that both CD5 + and CD5- B-lymphocyte subsets from either normal subjects or from IDDM patients receiving recombinant human insulin, contain B lymphocytes committed to the production of IA-IgM as a common element of their repertoire. In contrast, cells committed to the production of IA-IgG were only detected among the CD5- B lymphocyte subset from some IDDM patients. Only one microculture, out of a total of 6,211 screened (from control subjects and patients), in the CD5- B-cell subset from a recently-diagnosed IDDM patient, was found to produce ICA-IgM lambda. This might suggest that the frequency of circulating B lymphocytes committed to the production of ICA is very low even in IDDM patients bearing serum ICA. EBV-transformed B cells producing the ICA-IgM lambda were stabilized and cloned by somatic hybridization technique. This ICA-IgM lambda human monoclonal antibody, designated HY1-MB91, is not polyreactive, but shows a restricted reactivity with human pancreatic islets, failing to react with other human tissues including cerebellar cortex, and lacking rheumatoid factor and anti-DNA antibody activities. It also lacks reactivity with pancreatic islets from other mammalian species (rat, mouse and monkey) as well as with other rat tissues, including cerebellar cortex. The antigen recognized by HY1-MB91 antibody in human islet cells is a cytoplasmic component mostly found in beta cells.

Production of type II collagen specific monoclonal antibodies

Immunoassays are used for the specific measurement of type II collagen, a major cartilage protein, which is lost in osteoarthritic joints. Poor immunogenicity and species dependent immune response to type II collagen make it difficult to obtain specific antibodies required for immunoassay development. In addition, type II collagen antibodies exhibit reactivity to structurally dissimilar antigens such as actin, myoglobin, thyroglobulin and ssDNA, complicating the isolation of specific antibodies. It is therefore necessary to characterize the antibody reactivity against both noncollagenous antigens and different collagen types. In this study, immune response to type II collagen was improved by conjugation to carrier proteins, KLH and BSA. Hybridomas were generated by fusions of lymphocytes derived from lymph nodes or spleens with X63-653-Ag8 myeloma cells. Compared to spleens, the utilization of lymph nodes as a source of lymphocytes resulted in a 23% higher number of hybridomas secreting type II collagen antibodies. Hybridomas secreting polyreactive antibodies were identified based on their reactivity to thyroglobulin and eliminated. Extensive testing of the remaining monoclonal antibodies with other structurally dissimilar antigens and various types of collagen for reactivity, allowed us to isolate specific monoclonal antibodies to type II collagen. We emphasize the importance of characterization of the reactivity of type II collagen monoclonal antibodies before employing them for immunoassays.

Half-life of polyreactive antibodies

Monoclonal polyreactive antibodies bind to a variety of self and foreign antigens. In contrast, monoclonal monoreactive antibodies bind to a single or restricted number of known antigens. The rate at which polyreactive antibodies are removed from the circulation compared to monoreactive antibodies has not been determined. In the present experiments, human monoclonal polyreactive and monoreactive antibodies of different isotypes were injected intravenously into mice and the clearance from the circulation was determined. The half-life of polyreactive IgM, IgA, and IgG antibodies was 8.0, 8.2, and 9.8 hr, respectively, compared to 35.4, 26.6, and 280 hr for monoreactive IgM, IgA, and IgG antibodies, respectively. Examination of tissue sections from animals given intravenous antibody showed substantial deposition of polyreactive, but not monoreactive, antibodies in several organs, the liver being the principal site of deposition. It is concluded that polyreactive antibodies are cleared from the circulation substantially faster than monoreactive antibodies.

Cross-reactivity of IgG anti-DNA-secreting B cells in patients with systemic lupus erythematosus

This study is the first to analyze the cross-reactivity of in vivo activated B cells from patients with systemic lupus erythematosus. A chamber ELIspot assay was used to determine whether lymphocytes secreting antibodies that bound to DNA or 2,4,6-trinitrophenol (TNP)-keyhole limpet-hemocyanin (KLH) could simultaneously bind to the unrelated antigens actin or ovalbumin. IgM anti-DNA-, IgM anti-TNP-KLH- and IgG anti-TNP-KLH-secreting B cells from patients and controls showed similar levels of cross-reactivity (ranging from 6% to 23%, depending upon the antibody isotype and antigen pair examined). In general, IgG-producing cells were less cross-reactive than IgM producers from the same individual (on the average threefold, p < 0.001). In contrast, IgG anti-DNA-secreting B cells from lupus patients (i) showed no decrease in cross-reactivity when compared to IgM anti-DNA-secreting cells and (ii) were significantly more cross-reactive than control IgG anti-DNA-secreting cells and IgG anti-TNP-KLH secreting cells from patients (p < 0.001). The degree of IgG anti-DNA cross-reactivity correlated with disease activity (r = 0.52, p < 0.02). The implications of these findings with respect to repertoire expression and disease pathogenesis are discussed.

Serum and gingival crevicular fluid anti-desmosomal antibodies in periodontitis

SDS polyacrylamide gel electrophoresis separates desmosomal proteins and glycoproteins of bovine tongue epithelium by their relative molecular mass. The Western immunoblot technique was used to reveal the reactions of desmosomal proteins and glycoproteins with naturally occurring antibodies in serum and gingival crevicular fluid (GCF). Naturally-occurring serum and GCF antibodies (IgG and IgM) from periodontitis patients and healthy, unaffected controls reacted with desmosomal proteins (desmoplakins) and glycoproteins (desmogleins). Sera from 90% of subjects with periodontitis showed increased reactions of IgG with desmoplakins (240 and 210 kDa) and 80% with desmogleins (165, 130, and 115 kDa), when compared with unaffected controls. Patients' IgG reacted with desmosomal components more strongly than IgM. IgG antibodies against desmosomal antigens in GCF showed similar specificities from patients and healthy subjects and to their serums. When GCF within individuals with periodontitis was compared, anti-desmosomal IgG from diseased sites showed greater reactivity than healthy controls. These data suggest that anti-desmosomal antibodies are a normal part of the immune repertoire. The presence of elevated titers of anti-desmosomal antibodies appear to distinguish periodontitis from unaffected sites. When detected, elevated titers of anti-desmosomal antibodies may contribute to the pathogenesis and indicate increased risk of periodontitis.

CD5-positive B cells in type 1 (insulin-dependent) diabetic children

We have measured CD5+ B cell levels in the peripheral blood of 35 type 1 (insulin-dependent) diabetic children, aged 1.1-21.2 years (10.7 +/- 4.6 years). Patients were divided into two groups according to disease duration (group I < 6 months and group II > 1.5 years). Group I included 18 patients and group II 17 patients. Thirty-nine healthy subjects, comparable for age and sex, served as controls. CD5+ B cells were identified by double immunofluorescence staining with rhodamine-conjugated rabbit anti-human immunoglobulin and with a mouse anti-CD5 monoclonal antibody revealed by a fluorescein-conjugated goat anti-mouse immunoglobulin. We found that CD5+ B cell levels (expressed as percentages of peripheral blood B lymphocytes) were significantly higher in group I (median 24; range 4-48) than in controls (median 14; range 0-36, P < 0.001) and in group II (median 4; range 0-20, P < 0.001). A follow-up study of 12 group I patients showed a significant decline in CD5+ B cell levels. The data obtained in our diabetic patients suggest that CD5+ B cells are expanded in the early phase of type 1 diabetes mellitus and may play a role in the autoimmune process of the disease.

Characterization and measurement of CD5+ B cells in normal and Trypanosoma congolense-infected cattle

CD5+ B cells in cattle are present in peripheral blood and spleen, but not in lymph nodes, tonsils or Peyer's patches. Compared to classical B cells, they express similar levels of B cell surface markers, but have higher levels of surface IgM. We failed to find evidence for IgD on bovine B lymphocytes. The CD5+ B cells expressed CD11b (Mac-1). Another small subpopulation of B cells carried CD11b but not CD5. In cattle infected with Trypanosoma congolense, a dramatic increase in the percentage of CD5+ B cells in blood and spleen was observed. This increase occurred 7-10 days after parasites were first detected in the blood and correlated with the increase in serum IgM and the increase in the absolute number of B cells that is typical to trypanosome-infected animals. The increase in B cells was found to be due mainly to the expansion of the CD5+ B cell subpopulation. The cause of the amplification of the CD5+ B cells and their possible involvement in the production of autoantibodies and non-parasite-specific antibodies which have been described in trypanosome-infected animals are discussed.

Correlation of antibody multireactivity with variable region primary structure among murine anti-erythrocyte autoantibodies

A high proportion of the antibodies in the preimmune repertoire bind to several unrelated antigens and are considered to be multireactive. This property is reportedly associated with the antibodies produced by CD5+ B lymphocytes. Because many antibodies specific for bromelain-treated mouse red blood cells (BrMRBC) derive from CD5+ B cells, we tested monoclonal antibodies of this specificity for multireactivity. Two variable region combinations, VH11/V kappa 9 and VH12/V kappa 4, account for greater than 80% of this repertoire, but none of these antibodies exhibited a multireactive phenotype. In contrast, three anti-BrMRBC binding antibodies belonging to the J558 family (BrM1, BrM8, and CH12) showed varying degrees of multireactivity, and bound both highly negatively and positively charged antigens. The amino acid sequences of the VH regions of these antibodies are highly homologous (greater than 85% identical) and they possess large VH-D-J junctions with extensive N-region insertions. The kappa chains of two of these antibodies utilize an identical V kappa gene segment, while the third uses a very different V kappa with only 50% homology. The entire H chain V regions of these antibodies are unusually basic, with isoelectric points of 9.5-10, a feature which might be important in promoting interactions with acidic epitopes. The multireactive antibodies also contain regions with a high concentration of hydroxylside chain amino acids, especially in their VH-D-J junctions. This region also contains acidic amino acid residues, which may be important in binding of positively charged epitopes. We propose that an open, accessible binding site and a charge polarity may be features which facilitate the binding of charged epitopes, providing a structural basis for multireactivity of at least some antibodies.

Production of heterohybridomas secreting autoreactive and polyreactive human monoclonal antibodies

Peripheral blood lymphocytes from two polytransfused renal dialysis patients were transformed by Epstein-Barr virus, fused to a heteromyeloma and cloned. Eight human monoclonal antibodies from the resulting clones were tested for their binding to a variety of antigens by ELISA, indirect immunofluorescence and immunoblotting. Antigens tested included B-cell lines, T and B lymphocytes, red blood cells, chronic lymphocytic leukaemic B cells, IgG, ssDNA, dsDNA, histones, nucleoprotamine, sperm nuclei, thymus and spleen extracts, MOLT4 cell lysates, affinity purified autoantigens, tetanus toxoid, bacterial lipopolysaccharide, insulin, and a tissue section screen. These human monoclonal antibodies reacted with more than one antigen to varying degrees and were autoreactive and polyreactive. One of these heterohybridoma cell lines exhibited cytoplasmic staining with an anti-CD5 monoclonal. Our findings support the concept that in adult individuals a subset of B cells produce heterogeneous IgM antibodies which can bind to a variety of different autoantigens and also to foreign antigens. These monoclonals were different from the autoantibodies usually seen in renal dialysis patients in the sense that they were not lymphocytotoxic.

Aberrant T-regulation in rheumatoid arthritis and IgA nephropathy affects CD5+ and CD5- B lymphocytes equally

T-suppressor function and T-helper function in healthy adults, elderly patients with non-immune diseases, and patients with rheumatoid arthritis (RA) and IgA nephropathy (IgAN) were titrated by adding graded concentrations of CD8+ cells to autologous CD8-depleted peripheral blood mononuclear cells (PBMC), or CD4+ cells to CD8- 4- PBMC, respectively. Following culture with pokeweed mitogen (PWM), numbers of CD5+ and CD5- immunoglobulin-secreting cells were determined using a combination of rosetting with anti-CD5-coated Dynabeads and reverse haemolytic plaque formation (Jones, 1990). Of 11 RA patients studied, eight had slightly reduced suppressor activity for CD5+ and CD5- IgM-secreting cells, and three with active disease and high serum levels of C-reactive protein, could not suppress IgG, IgA or IgM secretion by either B subset. Helper activity for both CD5+ and CD5- B cells was slightly but significantly increased in RA patients. One of eight patients with IgAN could not suppress IgG, IgA or IgM production by CD5+ or CD5- B cells, and all IgAN patients required strikingly fewer CD4+ cells for PWM-induced activation of CD5+ and CD5- B cells than controls. It was concluded that in two immunologically mediated diseases in which some patients have raised numbers of circulating CD5+ B cells, aberrant T-regulation affects CD5+ and conventional CD5- B cells equally.

B cells expressing CD5 antigen are markedly increased in peripheral blood and spleen lymphocytes from patients with immune thrombocytopenic purpura

By two-colour flow cytometric analysis, we examined the proportion of B lymphocytes bearing CD5 cell surface antigen (CD 5+ B cells), which are capable of producing autoantibodies, both in peripheral blood and spleen from patients with chronic immune thrombocytopenic purpura (ITP). The percentage of CD5+ B cells in peripheral blood lymphocytes (PBLs) was significantly increased (P less than 0.005) in patients with ITP (3.7 +/- 2.2%, n = 30) as compared with normal controls (1.7 +/- 0.7%, n = 28). However, there was no correlation between the percentages of circulating CD5+ B cells and platelet counts. The percentage of splenic CD5+ B cells in ITP patients was much more increased (9.0 +/- 4.5%, n = 9), P less than 0.005) compared with that of other disorders (3.2 +/- 0.5%, n = 5). Furthermore, isolated splenic CD5+ B cells from two out of five ITP patients produced high levels of IgM-type, platelet-bindable antibodies (PBIgM) after stimulation with Staphylococcus aureus Cowan I (SAC), while CD5- B cells isolated from the same spleen or splenic CD5+ B cells from other non-autoimmune disorders failed to produce significant amount of PBIgM. In three ITP patients, no increase in PBIgM was detected despite SAC stimulation. The increased proportion of CD5+ B cells in peripheral blood and spleen, and their ability to produce anti-platelet antibodies indicate that they are directly involved in the autoimmune pathogenesis in ITP.

CD5+ B-lymphocytes are as dependent on T-helper cells and as responsive to T-suppressor cells in pokeweed mitogen-stimulated activation as conventional CD5- B-lymphocytes

Pokeweed mitogen (PWM)-stimulated cultures were established with varying numbers of CD4+ or CD8+ cells and CD5+ immunoglobulin-secreting cells were subsequently identified using a combination of haemolytic plaque formation and rosetting with immunobeads coated with anti-Leu-1. It was found that CD5+ and CD5- B-cells required similar numbers of CD4+ cells for half-maximum plaque-forming cell (PFC) induction and that 50% suppression of both CD5+ and CD5- PFC occurred with similar numbers of CD8+ cells. Suppression of both CD5+ and CD5- PFC could occur when T-helper signals were supplied by a PWM-stimulated culture supernatant, indicating that both subsets could be directly suppressed by CD8+ cells rather than by indirect suppression of T-helper cells. It is concluded that CD5+ B-cells are as responsive to T-regulatory influences as conventional CD5- B-cells.

Evidence for regulation of naturally activated autoreactive B cells

A large fraction of naturally activated B cells in the neonate displays degenerate specificity, including reactivity with autoantigens. Transgenic mouse models of autoreactive B cells are mainly concerned with monospecific B cells of high avidity, and the fate of naturally activated autoreactive B cells is still a matter of debate. To pursue this question further, we chose an IgM autoantibody with a recurrent idiotype (Id), i.e. Sp6, because transgenic mice expressing this IgM also were available. In a first approach monoclonal antibodies (mAb) derived from untreated, antigenically stimulated and transgenic mice were used to test whether there were indications for deletion or for Id regulation of naturally activated autoreactive B cells. Over 90% of thymus and spleen cell derived hybridomas from 6-day-old Sp6-transgenic mice were trinitrophenyl (TNP) reactive, carried the Sp6-Id and bound to a panel of self antigens, including mouse albumin. We failed to obtain B cell hybridomas from the thymus of 28-day-old Sp6-transgenic mice. Furthermore, we could not detect any mAb carrying an anti-Sp6 Id, but Sp6 did weakly bind to itself. About 25% of mAb derived from control mice displayed degenerate specificity, the majority of them also were TNP reactive. The Sp6 Id was found at a low frequency and a comparable number of mAb carried an anti-Sp6 Id. Prenatal manipulation at the antigen level (trinitrobenzenesulfonic acid treatment) led to a transient expansion of TNP- and autoreactive mAb. The number of mAb carrying the Sp6 Id was not increased, but mAb carrying an anti-Sp6 Id were observed at high frequency. Those mAb also displayed degenerate specificity. Since Sp6-transgenic mice were perfectly healthy, it is concluded that this particular autoreactive antibody of degenerate specificity cannot be harmful for the developing organism, which may possibly be due to its self-binding capacity. Furthermore, some process of down-regulation was indicated by the absence of B cells expressing the transgene in the thymus of young adult mice. Autoreactivity of untreated and prenatally antigen-treated mice was, in addition, regulated at the Id level. In particular, mAb recognizing the Id of Sp6 were significantly expanded in antigenically stimulated mice. The data were interpreted in the sense that autoreactive B cells appearing early during ontogeny were rather strictly controlled either by (functional) clonal deletion or by idiotypic connectivity.

Idiotypic profile of natural autoantibodies in newborn and young adult BALB/c mice

Idiotypic profiles of autoreactive monoclonal antibodies (MoAb) were evaluated by their reactivity with a panel of alkaline phosphatase (AP)-coupled detector MoAb derived from the same fusions. Attention was given to the question of whether differences exist between MoAb derived from spleen cells (SC) or thymocytes (TC) and whether ID profiles would change during post-natal development. In the newborn, natural autoantibodies and MoAb which did not react with any one of eight autoantigens displayed different ID profiles, autoreactive MoAb being characterized by the expression of a restricted pattern of ID. During post-natal development, changes of ID expression were only observed with autoreactive MoAb. Many ID which were detected on MoAb derived from 6-day-old mice were not detected on SC-derived MoAb from young adults, while a few ID were significantly over-represented. Furthermore, especially with TC-derived MoAb, a clear linkage between certain idiotypes and autoantigen specificities could be demonstrated. Thus, in contrast to non-autoreactive MoAb, natural autoantibodies in the young adult were characterized by expressing only a selected number of ID at high frequency. Furthermore, the B-cell environment apparently played a role, since there were marked differences between ID profiles of TC- versus SC-derived MoAb. The data are interpreted in the sense that expansion and maturation of naturally activated autoreactive B cells are controlled rather than being random processes.

Evaluation of CD5 and other differentiation antigens on human immunoglobulin-secreting cells using a combination of immunobead rosetting and reverse haemolytic plaque formation

This paper describes a new method, with high specificity and sensitivity, for evaluating cell surface markes such as differentiation antigens and cytokine receptors on immunoglobulin-secreting cells. Mononuclear cells, freshly derived from peripheral blood or following stimulation in vitro with pokeweed mitogen or Staphylococcus aureus Cowan I, are partially depleted of T cells and monocytes using immunomagnetic beads (Dynabeads) coated with anti-CD2. The cells are incubated with Dynabeads coated with monoclonal antibody against the cell marker under investigation and then used in a protein A haemolytic plaque assay. Plaque-forming cells (PFC) with (marker-positive) and without (marker-negative) attached beads can be readily enumerated. Values are given for percentages of IgG-, IgA- and IgM-PFC bearing CD19, CD38, CD25 and CD5.

CD5+ B lymphocytes, polyreactive antibodies and the human B-cell repertoire

The lock and key model of antigen-antibody reaction has traditionally been used to explain the specificity of antibodies and the need for antibody diversity. Recently it has become clear that certain antibodies are polyreactive and recognize a variety of self- and foreign antigens. It is now clear that these antibodies are made by a novel subset of B cells that bear the surface CD5 marker. Careful analysis has shown that about 20% of peripheral blood B lymphocytes in adults are CD5+ and, therefore, represent a major component of the normal human B-cell repertoire. The precise role of the antibodies produced by these cells is still not clear, but because of their polyreactivity they might function in clearing autoantigens from the circulation and/or as a rapid first line of defense against foreign invaders, such as bacteria and viruses. Sequence analysis showed that these antibodies use gene segments in germ-line configuration for their antigen-binding portion. In this article, Paolo Casali and Abner Notkins propose that polyreactive antibodies are what, for years, have been referred to as the 'natural antibodies' of serum and that under certain circumstances they may contribute to the pathogenesis of autoimmune diseases.

Monoreactive high affinity and polyreactive low affinity rheumatoid factors are produced by CD5+ B cells from patients with rheumatoid arthritis

In patients with rheumatoid arthritis (RA), circulating CD5+ B lymphocytes, but not CD5- B lymphocytes, are increased in number and size, exist in an activated state, spontaneously proliferate, and secrete Ig that binds to the Fc fragment of IgG. By constructing continuous mAb-secreting cell lines from CD5+ B lymphocytes, the properties and dissociation constants (Kd) of these antibodies were determined. Two types of rheumatoid factors (RFs) with discrete reactivities were produced. The first type is polyreactive and binds with relatively low affinity (Kd, 10(-5) mol/liter) to the Fc fragment of IgG. These antibodies are similar to those produced by CD5+ B cells from healthy subjects. The second type of RF is monoreactive and binds with higher affinity (Kd, 10(-7) mol/liter) to the Fc fragment of IgG. These latter autoantibodies are produced by CD5+ B cells of RA patients, but not healthy subjects. Long-term longitudinal studies are needed to determine the role of these two types of RFs in the pathogenesis of RA.