The nexus between atopic disease and autoimmunity: a review of the epidemiological and mechanistic literature

There has been considerable interest in defining the relationship between the expression of allergic and autoimmune diseases in populations of patients. Are patients with autoimmune disease 'protected' from developing allergic (immunoglobulin E-mediated) diseases? Does the establishment of an atopic phenotype reduce the risk of the subsequent development of autoimmune diseases? Although there are clinical studies addressing this question, methodological problems, particularly in identification of atopic subjects, limits their usefulness. Moreover, an immune-based explanation of the observed epidemiological findings has relied on a paradigm that is currently undergoing increased scrutiny and modification to include newly defined effector cell subsets and the interaction between genetic and environmental factors, such as early endotoxin or mycobacterial exposure. To address this question, we reviewed a series of clinical reports that addressed coincidence or co-prevalence of atopy with four autoimmune diseases: psoriasis, rheumatoid arthritis, multiple sclerosis and type I diabetes mellitus. We present a model whereby active T helper type 1 (Th1) inflammation may suppress the development of atopy, and atopy may suppress the severity but not necessarily the onset of autoimmunity, and then discuss our model in the context of mechanisms of adaptive immunity with particular reference to the Th1/Th2 paradigms. Because the ultimate goal is to ameliorate or cure these diseases, our discussion may help to predict or interpret unexpected consequences of novel therapeutic agents used to target autoimmune or atopic diseases.

Acetylcholine receptor alpha subunit mRNA expression in human thymus: augmented expression in myasthenia gravis and upregulation by interferon-gamma

Previous studies by us and others have demonstrated the expression of acetylcholine receptors on epithelial cells in the thymus of myasthenia gravis (MG) and control subjects. In the present experiments, we used a reverse transcription-polymerase chain reaction (RT-PCR) to analyze the profile of the two major isoforms of the alpha chain of these receptors (AChRalpha), P3A- and P3A+, in thymus tissue obtained from MG and control subjects and a human thymic epithelial cell line (TEC9). In addition, using a semiquantitative RT-PCR, we compared the amounts of P3A- and P3A+ mRNA expressed in thymic tissue obtained from these two sources and determined if their expression in TEC9 is modulated by cytokines. We found that mRNAs encoding P3A- and P3A+ are expressed at approximately a 5:1 ratio in both MG and control thymus tissue. This contrasts with skeletal muscle where mRNAs encoding these isoforms are expressed equally. A pattern of preferential P3A- vs P3A+ mRNA expression was also observed in TEC9. We observed 2.8-fold greater expression of both isoforms in MG than in control thymus. Expression of both isoforms in TEC9 was enhanced significantly by treatment with interferon-gamma whereas IL-1alpha, IL-4, and IL-6 had no effect. Thus, there is differential regulation of AChRalpha variants in thymus and TEC relative to muscle and interferon-gamma represents a novel regulator of AChRalpha mRNA expression. MG thymus is distinguished by increased expression of both isoforms of this autoantigen, a finding that may reflect enhancement of transcription by local microenvironmental factors.

In vivo inflammatory response to a prototypic B cell superantigen: elicitation of an Arthus reaction by staphylococcal protein A

Staphylococcal protein A (SpA) is representative of a new class of Ags, the B cell superantigens (SAgs). These SAgs, unlike conventional Ags, bind to the Fab regions of Ig molecules outside their complementarity-determining regions. In addition, B cell SAgs can react with a substantial amount of a host's serum Igs by virtue of their ability to interact with many members of an entire variable heavy chain (VH) or variable light chain gene family. For example, SpA reacts with the Fabs of most human Igs using heavy chains from the VH3 gene family (VH3+). Members of this gene family are expressed on 30 to 60% of human peripheral B cells. We sought to determine whether the interaction of a B cell SAg with its reactive Igs can elicit immune complex-mediated tissue injury. Using the Arthus reaction in rabbits as an in vivo model of immune complex-mediated tissue inflammation, we demonstrated that untreated rabbits, which were administered SpA intradermally (i.d.), do not develop a cutaneous inflammatory response. However, when rabbits were pretreated i.v. with human IgG (hIgG), i.d. injections of SpA induced an inflammatory response with the classical histologic features of an Arthus reaction. To determine whether this Arthus-like response occurred via a B cell superantigenic mechanism, the rabbits were pretreated with VH3-depleted hIgG and then were administered SpA i.d. We found that the induction of a prominent inflammatory response by SpA was dependent upon the presence of VH3+ molecules in the hIgG pretreatment. These results provide compelling evidence that an interaction of the B cell SAg, SpA, with its reactive (VH3+) IgGs leads to an immune complex-mediated inflammatory response in vivo.

Complement activation by a B cell superantigen

Staphylococcal protein A (SpA), acting as a B cell superantigen, binds to the Fab region of human VH3+ Igs. Using SpA abrogated of its IgG Fc binding activity (Mod SpA) as a model B cell superantigen, we determined whether such an interaction causes complement activation. Addition of Mod SpA to human serum led to complement consumption and the generation of C3a. To determine whether this complement activation 1) was due to an interaction between VH3+ Igs and the Fab binding site of SpA and 2) proceeded via the classical complement pathway, we tested a panel of monoclonal IgM proteins for the ability to hind C1q following interaction with SpA. C1q binding was restricted to SpA-reactive, VH3+ IgM proteins. To formally determine whether the binding of SpA to the reactive VH3+ IgM proteins led to complement activation, we reconstituted the serum from a hypogammaglobulinemic patient with monoclonal IgM proteins and measured complement consumption and C3a generation following the addition of Mod SpA. We observed complement consumption and C3a production only in Mod SpA-treated serum reconstituted with a VH3+, SpA-binding, IgM protein. Taken together, these results provide compelling evidence that the interaction of the Fab binding site of SpA and VH3+ Igs can lead to complement activation via the classical pathway. This novel interaction may have significant implications for the in vivo properties of a B cell superantigen.

Complement activation by a B cell superantigen

Staphylococcal protein A (SpA), acting as a B cell superantigen, binds to the Fab region of human VH3+ Igs. Using SpA abrogated of its IgG Fc binding activity (Mod SpA) as a model B cell superantigen, we determined whether such an interaction causes complement activation. Addition of Mod SpA to human serum led to complement consumption and the generation of C3a. To determine whether this complement activation 1) was due to an interaction between VH3+ Igs and the Fab binding site of SpA and 2) proceeded via the classical complement pathway, we tested a panel of monoclonal IgM proteins for the ability to hind C1q following interaction with SpA. C1q binding was restricted to SpA-reactive, VH3+ IgM proteins. To formally determine whether the binding of SpA to the reactive VH3+ IgM proteins led to complement activation, we reconstituted the serum from a hypogammaglobulinemic patient with monoclonal IgM proteins and measured complement consumption and C3a generation following the addition of Mod SpA. We observed complement consumption and C3a production only in Mod SpA-treated serum reconstituted with a VH3+, SpA-binding, IgM protein. Taken together, these results provide compelling evidence that the interaction of the Fab binding site of SpA and VH3+ Igs can lead to complement activation via the classical pathway. This novel interaction may have significant implications for the in vivo properties of a B cell superantigen.

Practice parameters for the diagnosis and management of immunodeficiency. The Clinical and Laboratory Immunology Committee of the American Academy of Allergy, Asthma, and Immunology (CLIC-AAAAI)

In this brief review, only the most useful immunologic tests available for defining host defects that lead to susceptibility to infection have been emphasized. It should be pointed out that those evaluations and tests ordered by the physician will rule out the vast majority of the currently recognized defects. Finally, it is important that any patients identified as abnormal by these screening tests be characterized as fully as possible in centers specializing in these diseases before therapy is initiated, since what may appear to be a simple diagnosis on the surface may be an indicator of more complex underlying problems.

B-cell superantigens: definition and potential impact on the immune response

Superantigens have been extremely helpful tools in exploring fundamental questions in immunobiology including mechanisms of cell activation, tolerance, and autoimmunity. Until recently, attention has been focused exclusive on T-cell superantigens. However, new data suggest that there are superantigens that directly activate B cells. By definition, these agents (1) stimulate a high frequency of B cells, (2) target B cells that have restricted usage of VH or VL family genes, and (3) bind to immunoglobulins outside the sites that bind conventional antigens. A candidate B-cell superantigen that has received considerable attention in this laboratory is staphylococcal protein A. This agent is best known to the immunologist because of its ability to bind to the Fc fragment of IgG. This binding has been localized to two alpha-helical structures on each of four or five homologous regions that comprise the extracellular domain of protein A. However, it is now clear that protein A contains a second site that binds to determinants on the Fab regions of certain immunoglobulins independently of their heavy-chain isotype. In man this so-called alternative site appears to bind only to immunoglobulins that utilize heavy-chain genes of the VH3 subfamily. In the mouse this type of binding is restricted to immunoglobulins using heavy chains belonging to the S107 and J606 VH families. In this review, we examine the growing list of microbial products that dominate B-cell superantigenic properties. Using staphylococcal protein A as a model for a B-cell superantigen, we consider the potential impact of this novel class of antigens on the immune response. We focus on the ability of B-cell superantigens to influence the expression of the B-cell repertoire. In addition, we consider the hypothesis that the interaction of a B-cell superantigen with its reactive serum immunoglobulins activates the classical complement cascade and thus represents a powerful stimulant of tissue inflammation.

Staphylococcus aureus Cowan I-induced human immunoglobulin responses: preferential IgM rheumatoid factor production and VH3 mRNA expression by protein A-binding B cells

Protein A (PA), a cell wall component of SAC, activates human B cells by cross-linking the Fabs of membrane immunoglobulins. Recent data indicate that PA binds only to Fabs that use VH3 heavy chains, and thus it has been designated as a B-cell superantigen. We previously reported that Staphylococcus aureus Cowan I (SAC)-induced IgM rheumatoid factor (RF) by human PBMC was mediated by PA. Therefore, we sought to determine if SAC-induced IgMRF production was confined to PA-binding B cells and if these B cells were enriched for the expression of VH3 heavy chains. We observed that the elicitation of IgMRF in response to SAC was limited to a subset of B cells that bind PA and that this subset was enriched for VH3 mRNA expression. Taken together, these results suggest that IgMRFs produced in response to SAC are enriched for usage of VH3 heavy chains. Thus, this SAC-induced autoantibody response appears to represent a new B-cell superantigenic property of PA.

Serum tryptase in idiopathic anaphylaxis: a case report and review of the literature

Anaphylaxis is a life-threatening disease that characteristically presents with multiple arrays of dermatologic, respiratory, cardiovascular, and gastrointestinal derangements, in general, suddenly after exposure to an allergen. It can, however, occur without an identifiable precipitant or event, and this well-defined entity has been called idiopathic anaphylaxis. The diagnosis of idiopathic anaphylaxis is made after an appropriate allergic evaluation and exclusion of a provocative trigger. We report an unusual case of manifesting with gastroenteritis, urticaria, hypotension, and syncope. Measurement of serum tryptase, a mast cell enzyme, was used to substantiate the diagnosis. Tryptase level is a useful test that can be used to help diagnose this potentially fatal disease.

The high affinity Fc gamma receptor (CD64) induces phagocytosis in the absence of its cytoplasmic domain: the gamma subunit of Fc gamma RIIIA imparts phagocytic function to Fc gamma RI

The high affinity Fc gamma receptor, Fc gamma RI, is unique among the three classes of macrophage Fc gamma receptors not only in its affinity for IgG, but also in the structure of its cytoplasmic domain. Fc gamma RIIA and the gamma subunit of Fc gamma RIIIA have tyrosine-containing motifs within their cytoplasmic domains that are phosphorylated when crosslinked and that are required for phagocytosis by COS-1 cell transfectants. In contrast to these other Fc gamma receptors, Fc gamma RI does not contain cytoplasmic tyrosines and does not induce phagocytosis in COS-1 transfectants. We transfected wild-type (WT) and mutant (MT) Fc gamma RI lacking the cytoplasmic domain into COS-1 cells and murine macrophages and assessed phagocytosis using IgG-coated red blood cells (RBCs) and RBCs conjugated with Fab anti-human Fc gamma RI monoclonal antibody (mAb). Fc gamma RI, in contrast to Fc gamma RIIA, did not induce phagocytosis in COS cells. However, both WT and MT Fc gamma RI induced phagocytosis in murine macrophages, and phagocytosis was inhibited by the tyrosine kinase inhibitor tyrphostin 23. Human monocytes also phagocytosed Fc gamma RI-targeted RBCs, and activation of Fc gamma RI on monocytes with Fab anti-Fc gamma RI induced phosphorylation of Fc gamma RII on tyrosine residues. However, Fc gamma RI activation of Fc gamma RI-Fc gamma RIIA COS-1 cotransfectants did not induce tyrosine phosphorylation of Fc gamma RIIA, and coexpression of Fc gamma RI and Fc gamma RIIA in COS cells did not confer Fc gamma RI phagocytic capability. In contrast, coexpression in COS-1 cells of Fc gamma RI with the gamma subunit of Fc gamma RIIIA conferred phagocytic function to both Fc gamma RI and the MT Fc gamma RI lacking the cytoplasmic domain. Thus, Fc gamma RI does not require its cytoplasmic domain to mediate a phagocytic signal and interacts with the gamma subunit of Fc gamma RIIIA to induce phagocytosis.

Insertion of cytoplasmic tyrosine sequences into the nonphagocytic receptor Fc gamma RIIB establishes phagocytic function

Receptors for the Fc domain of IgG on cells of hematopoietic lineage perform important functions, including stimulation of the ingestion of IgG-coated cells. In examining the function of Fc gamma receptor isoforms by transfection into COS-1 cells, we have observed that Fc gamma RIIA induces the binding and phagocytosis of IgG-sensitized RBCs (EA) and that transfected COS-1 cells can serve as a model for examining the molecular structures involved in mediating a phagocytic signal. We now report that COS-1 cell transfectants expressing the isoforms Fc gamma RIIB1 and Fc gamma RIIB2 and a Fc gamma RIIA mutant without a cytoplasmic tail efficiently bind EA but do not mediate their phagocytosis. Furthermore, wild-type Fc gamma RIIA, but not Fc gamma RIIB1 or Fc gamma RBII2, was phosphorylated on tyrosine upon receptor activation. Tyrphostin 23, which alters tyrosine kinase activity, inhibited the phagocytosis of EA and reduced the phosphorylation of Fc gamma RIIA on tyrosine. Fc gamma RIIB1 and Fc gamma RIIB2 contain one copy of the cytoplasmic sequence YXXL/I implicated in signal transduction, whereas Fc gamma RIIA contains two copies. We therefore inserted YXXL/I sequences at different sites in Fc gamma RIIB2. Low levels of phagocytosis were observed in a Fc gamma RIIB2 mutant bearing the Fc gamma RIIA sequence YMTL and higher levels of phagocytosis were observed in a second Fc gamma RIIB2 mutant that contained both the upstream YMTL and an additional downstream tyrosine-containing motif. Activation of this mutant receptor also induced receptor tyrosine phosphorylation. Thus, these studies indicate that both the number and placement of YXXL sequences in the cytoplasmic domain of the Fc gamma RII receptor family affect both receptor tyrosine phosphorylation and phagocytic competence.

Polyautoimmune syndrome in common variable immunodeficiency

Common variable immunodeficiency (CVI) is a heterogenous disorder with hypogammaglobulinaemia and multiple bacterial infections primarily involving the sinopulmonary tract. CVI patients have been known to have an increased tendency to develop autoimmune manifestations. Commonly associated autoimmune diseases include immune thrombocytopenic purpura, autoimmune haemolytic anaemia, and rheumatoid arthritis. In this paper we report a case of CVI presenting with multiple unusual autoimmune diseases including parotitis, vitiligo, atrophic gastritis, pernicious anaemia, and primary biliary cirrhosis. To our knowledge, this is the first case of CVI with polyautoimmunity and antimitochondria antibody. Recognition of this association is important because early diagnosis and treatment can greatly influence the prognosis.

Hypogammaglobulinemia and rheumatic disease

Primary hypogammaglobulinemia describes a heterogeneous group of immunoglobulin disorders mainly composed of X-linked agammaglobulinemia, common variable immunodeficiency, and selective immunoglobulin (Ig) A deficiency. The most serious problems are related to recurrent infections with high-grade encapsulated bacteria. However, a wide variety of rheumatologic disorders also occur in association with hypogammaglobulinemic states. Septic arthritis with usual bacterial pathogens such as Staphylococcus aureus, and unusual bacteria such as Mycoplasma and Ureaplasma species, have been described in these patients. An aseptic nonerosive polyarticular arthritis that resembles rheumatoid arthritis is seen in 10% to 30% of hypogammaglobulinemic patients. Autoimmune disorders such as immune thrombocytopenic purpura, immune hemolytic anemia, juvenile rheumatoid arthritis, systemic lupus erythematosus, dermatomyositis, Sjögren's syndrome, essential mixed cryoglobulinemia, chronic active hepatitis, and sarcoidosis have been reported in hypogammaglobulinemic patients. Finally, to complicate matters, many disease-modifying antirheumatic drugs, including gold, D-penicillamine, sulfasalazine, azathioprine, and cyclophosphamide, cause symptomatic hypogammaglobulinemia in some patients.

Calcium signalling by the high affinity macrophage Fc gamma receptor requires the cytosolic domain

Hematopoietic cells express multiple receptors which bind the Fc domain of IgG. We utilized transfection of COS-1 cells, a cell line which lacks endogenous Fc receptors, to study the expression and function of Fc gamma RI, the high affinity Fc gamma receptor in the absence of other Fc gamma receptors. Fc gamma RI was efficiently expressed in transiently transfected COS-1 cells as measured by flow cytometry and the binding of IgG sensitized RBCs (EA). In addition, analysis at the single cell level demonstrated that individually transfected COS-1 cells release cytosolic free Ca2+ [(Ca2+)i] upon activation with anti-Fc gamma RI antibody. The calcium response required Fc gamma RI cross-linking. COS-1 cells transfected with mutant Fc gamma RI lacking the cytosolic domain expressed Fc gamma receptors and bound EA as well as wild type receptors, but failed to induce an increase in [Ca2+]i. These data indicate that Fc gamma RI in the absence of other Fc gamma receptors mediates a calcium signal and that the cytoplasmic domain of Fc gamma RI contains the elements required for calcium dependent signal transduction.

Molecular evidence for the expression of nicotinic acetylcholine receptor alpha-chain in mouse thymus

The presence and structure of nicotinic acetylcholine receptor (nAChR) in the thymus has been a subject of interest for many years because of its possible role in the pathogenesis of the autoimmune disease myasthenia gravis. Using the polymerase chain reaction with primers specific for the alpha-chain of nAChR (nAChR-alpha), an 880-bp homologous band was found after amplification of cDNA prepared from mouse thymus, thymic medullary and cortical epithelial cell lines, but not from thymocytes or kidney. Sequencing of the polymerase chain reaction product from the thymus and thymic medullary and cortical epithelial lines showed identity with skeletal muscle nAChR-alpha over the region examined. This region includes the domains of the molecule on which B cell and T cell autoantigenic targets have been described. No evidence was found in mouse tissue for the exon 3A, which has been described in human muscle and the human rhabdomyosarcoma cell line TE671. Our results provide evidence at the RNA level for the expression of the nAChR-alpha on stromal cells but not on thymocytes in normal murine thymus and are consistent with a role for intrathymic autoantigen expression in the pathogenesis of myasthenia gravis.

Molecular evidence for the expression of nicotinic acetylcholine receptor alpha-chain in mouse thymus

The presence and structure of nicotinic acetylcholine receptor (nAChR) in the thymus has been a subject of interest for many years because of its possible role in the pathogenesis of the autoimmune disease myasthenia gravis. Using the polymerase chain reaction with primers specific for the alpha-chain of nAChR (nAChR-alpha), an 880-bp homologous band was found after amplification of cDNA prepared from mouse thymus, thymic medullary and cortical epithelial cell lines, but not from thymocytes or kidney. Sequencing of the polymerase chain reaction product from the thymus and thymic medullary and cortical epithelial lines showed identity with skeletal muscle nAChR-alpha over the region examined. This region includes the domains of the molecule on which B cell and T cell autoantigenic targets have been described. No evidence was found in mouse tissue for the exon 3A, which has been described in human muscle and the human rhabdomyosarcoma cell line TE671. Our results provide evidence at the RNA level for the expression of the nAChR-alpha on stromal cells but not on thymocytes in normal murine thymus and are consistent with a role for intrathymic autoantigen expression in the pathogenesis of myasthenia gravis.

The immunobiology of human Fc gamma receptors on hematopoietic cells and tissue macrophages

The ability to identify and remove potentially dangerous foreign organisms and proteins is critical to the survival of a species. In humans, IgG antibodies serve to recognize such foreign antigens and to facilitate their removal. The latter process involves several hematopoietic cells, including those of the macrophage phagocytic system, which express Fc gamma receptors. These receptors specifically recognize the Fc domain of IgG antibody. On the surface of hematopoietic cells these Fc gamma receptors mediate cell attachment and stimulate several signal transduction events, including those which lead to phagocytosis. Moreover, their perturbation can lead to the generation and release of mediators and enzymes involved in inflammation and in the pathogenesis of autoimmune diseases.

The use of IVIG in neurological disease

The studies cited herein highlight the potential benefits of IVIG therapy in a group of neurological disorders that are associated with aberrant immune responses. Indeed, all of the disorders discussed, except epilepsy, are associated with autoreactivity. The trials are preliminary and short-term and, except for idiopathic CIDP, uncontrolled. Interpretation of the findings of these uncontrolled studies is complicated by the fact that the natural history of all of these disorders is to show fluctuations. IVIG appears to be a potentially useful and safe agent in the treatment of patients with MG, intractable epilepsy, MS, and CIDP. Its place in the therapeutic approach to these neurological diseases must await the completion of controlled trials. Since other therapeutic modalities have already proven to be useful in several of these disorders, it will be important to determine if IVIG is more efficacious, safer, and more cost-effective. It is also worth considering whether the combination of IVIG and any of these more traditional approaches would provide added therapeutic benefit.

Human Fc gamma RII, in the absence of other Fc gamma receptors, mediates a phagocytic signal

Fc gamma receptors are important components in the binding and phagocytosis of IgG-sensitized cells. Studies on the role of these receptors have been limited by the fact that most hematopoietic cells express more than one Fc gamma receptor. We studied the role of Fc gamma RIIA in isolation on a human erythroleukemia cell line (HEL) which expresses Fc gamma RIIA as its only Fc gamma receptor. HEL cells were observed to bind and phagocytose IgG-sensitized red blood cells (RBCs) in a dose-dependent manner. We then examined the role of Fc gamma RI and Fc gamma RII in isolation and in combination, in transfected COS-1 cells. Fc gamma RIIA-transfected COS cells also mediated both the binding and phagocytosis of IgG-sensitized RBCs. In contrast, phagocytosis was not observed in Fc gamma RI-transfected cells, although these cells avidly bound IgG-sensitized RBCs. Furthermore, coexpression of both receptors by doubly transfected cells did not affect the phagocytic efficiency of Fc gamma RIIA. These studies establish that Fc gamma RIIA can mediate phagocytosis and suggest that transfected COS-1 cells provide a model for examining this process. Since HEL cells exhibit characteristics of cells of the megakaryocyte-platelet lineage, including expression of Fc gamma RII as the only Fc gamma receptor, Fc gamma RIIA on megakaryocytes and platelets may be involved in the ingestion of IgG-containing immune complexes. Furthermore, these studies indicate that Fc gamma RI and Fc gamma RIIA differ in their requirements for transduction of a phagocytic signal.

Pokeweed mitogen-induced immunoglobulin secretory responses of thymic B cells in myasthenia gravis: selective secretion of IgG versus IgM cannot be explained by helper functions of thymic T cells

The thymus, with its striking B cell infiltrates, is widely regarded as an important element in the pathogenesis of myasthenia gravis (MG) but its role remains to be elucidated. To gain further insight into the functional properties of MG thymic B cells, we studied the heavy chain isotype of immunoglobulin they produced in vitro in response to the T cell-dependent polyclonal activator pokeweed mitogen (PWM). MG thymic cells secreted prominent amounts of IgG but little IgM. In contrast, peripheral blood mononuclear cells (PBM) of the same subjects secreted similar amounts of IgG and IgM as did PBM of control subjects. In cell admixture experiments, MG thymic T cells, like PBM T cells, helped autologous PBM B cells produce IgM as well as IgG, although the overall magnitude of help for both isotypes appeared less than that of PBM T cells. Thus, in response to PWM, MG thymic B cells are largely committed to an IgG response and this likely reflects the intrinsic properties of these cells rather than the immunoregulatory properties of thymic T cells. This IgG isotype switch likely reflects in vivo activation events.

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.

Lymphocyte subpopulations in children with abnormal lymphatic circulation

Peripheral blood lymphocyte subsets were enumerated in five children with abnormal lymphatic circulation (three with lymphangiectasia, one with chylothorax, and one child with chyloperitoneum). All patients were lymphopenic. The percentage and absolute number of blood T-lymphocytes (CD3) were low in two children and normal in the other children. The percentage and absolute number of helper/inducer lymphocytes (CD4) were markedly reduced in all patients. The percentage of suppressor/cytotoxic lymphocytes (CD8) was normal or elevated in all children, and the absolute number of CD8 cells was normal in three patients. The CD4/CD8 ratio was reversed in all patients. In the two patients tested, the proliferative response of peripheral blood mononuclear cells to mitogens was reduced. T-lymphocyte subsets were measured in the pleural or peritoneal fluid of three patients, and the CD4/CD8 ratio was normal or increased. In each child, the CD4/CD8 ratio in the lymphatic fluids was markedly higher than the CD4/CD8 ratio of the blood (4.0/0.45, 1.75/0.95, and 1.3/0.85). The reversed CD4/CD8 ratio in the blood in cases of chronic loss of chyle may be due to either selective transport of CD4 lymphocytes into the lymphatic fluids or a shorter half-life of CD8 compared to CD4 lymphocytes. This finding may in part explain the abnormal cellular immunity previously observed in patients with lymphangiectasia.

Monocyte Fc gamma receptor recognition of cell-bound and aggregated IgG

Monocyte and macrophage Fc gamma receptors are important components in the recognition of IgG-coated cells and IgG-containing immune complexes. Two proteins have been identified on human peripheral blood monocytes that can function as Fc gamma receptors, Fc gamma RI (70 Kd) and Fc gamma RII (40 Kd). We studied the role of Fc gamma RI and Fc gamma RII on human monocytes by examining their binding of IgG-sensitized cells (human IgG anti-D-coated RBCs and rabbit IgG-sensitized sheep RBCs) and their binding of human trimeric IgG. To examine the function of monocyte Fc gamma RII, we used an anti-Fc gamma RII monoclonal antibody (MoAb) that competes for the Fc gamma RII ligand binding site. Preincubation of monocytes with saturating concentrations of anti-Fc gamma RII MoAb did not alter the recognition of IgG (anti-D)-sensitized human RBCs by monocytes. Furthermore, ligand-binding studies demonstrated that anti-Fc gamma RII antibody altered neither the number nor the affinity of monocyte-binding sites for human IgG trimer. Anti-Fc gamma RII inhibited monocyte binding of rabbit IgG-sensitized sheep RBCs, but only at low ionic strength or temperature when increased numbers of monocyte Fc gamma RII were expressed. At low ionic strength and 4 degrees C, anti-Fc gamma RII also partially inhibited monocyte binding of human trimeric IgG. Thus, monocyte Fc gamma RII does not appear to recognize IgG-sensitized RBCs or trimeric IgG at physiologic temperatures and ionic strength. The data suggest that Fc gamma RI is the primary Fc gamma receptor on monocytes involved in the binding of IgG (anti-D)-sensitized erythrocytes and low mol wt complexes of IgG.

Phenotypic characteristics of thymic B lymphocytes in myasthenia gravis

We have found prominent secretion of immunoglobulin and anti-acetylcholine antibodies by thymic lymphocytes (TL) of myasthenics despite a relative paucity of B (surface IgM+) cells in such TL. To determine whether there was a surface IgM- B cell in the TL which could manifest such responses, we compared the frequency of cells expressing the B cell-specific phenotypic marker CD20 (B1+), surface IgM (SIgM+), surface IgG (SIgG+), and surface IgD (SIgD+) in TL and autologous blood mononuclear cells in 36 myasthenic patients. B1+ cells were significantly more frequent than SIgM+ cells in TL (3.2 +/- 0.6 vs 0.6 +/- 0.2). In double-labeling studies, less than 25% of the B1+ cells coexpressed SIgM. Only 0.3% of the TL were SIgD+. In contrast, the frequencies of B1+ and SIgM+ cells in autologous blood were not significantly different (10.7 +/- 1.3 vs 8.2 +/- 0.8%). About 75% of blood B1+ cells co-expressed SIgM. These findings suggest that mast B cells in these TL have undergone isotope switching during prior in vivo differentiation and could manifest the observed humoral responses.

Neurologic complications of collagen vascular diseases

Despite the importance of neurologic manifestations of the collagen vascular diseases, it is clear that there are more questions than answers. The use of in vitro culture systems, in vivo models, and clinical and laboratory study of patients that attempt to correlate these findings with immunologic abnormalities, including parallels with animal models, should increase our understanding of these syndromes.

Evaluation of B-cell immunity in patients with pretransplant sensitization

The influence of presensitization (blood transfusions) on B-cell immunity as reflected in the serum of two groups of candidates for cadaveric donor renal allografts was examined. The first group initially had a high level of panel-reactive antibody (PRA) greater than 72% but experienced a large decrease in PRA (greater than 70%) 6-34 months prior to transplantation. In contrast, the second group maintained a high PRA (100%) for up to 28 months after sensitization and before transplantation. Three blood Three blood samples from each patient, representing a maximum time span of 34 months, were analyzed. Levels of IgG, IgM isohemagglutinins, and antitetanus antibody were used as indicators of B-cell function. There were no significant differences between the individual values of a single patient with regard to each parameter. However, Group II patients had elevated values of total IgG relative to Group I patients. Total serum IgG-subclass levels (IgG1, IgG2, IgG3, IgG4) were measured and the relationship between a specific IgG subclass and the PRA activity was determined. IgG1 values in Group II were higher than those found for Group I. The other IgG subclasses were all within normal levels and were not significantly different between Group I and Group II. When IgG-subclass typing of PRA was performed, IgG1 accounted for most of the activity in both groups and a fall in PRA-specific IgG1 was associated with the reduced PRA observed in Group I. The data indicate that humoral immunity, as reflected by total and specific immunoglobulin levels, is intact in general in the two groups of presensitized renal allograft candidates examined and that any loss of PRA activity reflects a reduction in a specific immune response.

In vitro IgM rheumatoid-factor production induced by tetanus toxoid

In vitro stimulation of lymphocytes from healthy donors with well-defined polyclonal B cell activators may elicit the production of rheumatoid factor (RF) as well as other autoantibodies. Antigen stimulation may also result in polyclonal B cell activation, but it is not known if RF production is a feature of this response. Therefore, peripheral blood mononuclear cells from 36 healthy volunteers previously immunized to tetanus toxoid (TT) were stimulated in vitro for 9 days with a conventional antigen, TT, or pokeweed mitogen, a standard polyclonal B cell activator. Culture supernatants were analyzed for total IgG, total IgM, and IgM RF by ELISA. TT-induced IgM RF production was observed in 10/36 experiments compared to 18/36 experiments in which cells were cultured with pokeweed mitogen, with a similar magnitude of response to these respective stimulants. The in vitro IgM-RF response to TT did not require a recent in vivo TT booster immunization and was observed at an antigen does that elicits polyclonal B cell activation but not IgG specific anti-TT antibody. TT-induced IgM RF responder cultures demonstrated higher levels of total IgG and total IgM production than cultures not secreting IgM RF in response to TT. These results indicate that IgM RF production is a concomitant of the polyclonal B cell response elicited by a conventional antigen. Unlike other model systems, this antigen-induced RF response was not mediated by the action of IgG antibody containing immune complexes.

Prominent IgM rheumatoid factor production by human cord blood lymphocytes stimulated in vitro with Staphylococcus aureus Cowan I

We previously reported that Staphylococcus aureus Cowan I (SAC) is a potent stimulant of IgM rheumatoid factor (RF) production by normal adult peripheral blood mononuclear cells. In the current study, we compared the capacity of normal adult peripheral blood mononuclear cells and cord blood mononuclear cells to produce IgM RF. Although both populations of cells consistently produced IgM RF in response to SAC, the quantity of RF produced by cord blood cells (128 +/- 18 ng/ml, mean +/- SEM) greatly exceeded that of adult cells (37 +/- 5 ng/ml, p less than 0.0005) even though both populations of cells demonstrated comparable total IgM responses. Remarkably, 16.7% of total IgM produced by cord blood cells in response to SAC showed RF activity compared to only 3.4% (p less than 0.0001) of the total IgM produced by SAC-stimulated adult cells. Thus, precursors of IgM RF-secreting cells are not only a consistent feature of the normal adult human B cell repertoire, but they are especially represented at the time of birth. These findings are consistent with the hypothesis that IgM RF originates from germ line genes and underscore the utility of SAC as a probe for analyzing the production of this autoantibody.

Prominent IgM rheumatoid factor production by human cord blood lymphocytes stimulated in vitro with Staphylococcus aureus Cowan I

We previously reported that Staphylococcus aureus Cowan I (SAC) is a potent stimulant of IgM rheumatoid factor (RF) production by normal adult peripheral blood mononuclear cells. In the current study, we compared the capacity of normal adult peripheral blood mononuclear cells and cord blood mononuclear cells to produce IgM RF. Although both populations of cells consistently produced IgM RF in response to SAC, the quantity of RF produced by cord blood cells (128 +/- 18 ng/ml, mean +/- SEM) greatly exceeded that of adult cells (37 +/- 5 ng/ml, p less than 0.0005) even though both populations of cells demonstrated comparable total IgM responses. Remarkably, 16.7% of total IgM produced by cord blood cells in response to SAC showed RF activity compared to only 3.4% (p less than 0.0001) of the total IgM produced by SAC-stimulated adult cells. Thus, precursors of IgM RF-secreting cells are not only a consistent feature of the normal adult human B cell repertoire, but they are especially represented at the time of birth. These findings are consistent with the hypothesis that IgM RF originates from germ line genes and underscore the utility of SAC as a probe for analyzing the production of this autoantibody.

B cell activation in multiple sclerosis

A microtechnique was established for the study of the limited numbers of cells available in CSF. The method allowed for the determination of the number of immunoglobulin-secreting cells (IgSC) as well as the quantitation of immunoglobulin or specific antibody secreted into the culture medium. Dose-response curves and kinetic profiles for the IgSC responses induced by pokeweed mitogen (PWM), a polyclonal B cell activator, were similar for CSF cells (CSFC) and peripheral blood mononuclear cells (PBMC). When equal numbers of unstimulated CSFC and PBMC from patients with multiple sclerosis (MS) were cultured, both the number of IgSC and the amount of secreted IgG were significantly greater in CSFC cultures. The addition of PWM resulted in the differentiation of B cells among both CSFC and PBMC, as shown by an increase of both the number of IgSC and the amount of secreted IgG. Results with cultures of unstimulated cell suspensions from MS patients suggested that CSF cells from these patients may be activated in vivo. The addition of mitomycin-C treated autologous peripheral blood mononuclear cells (PBMCM) to cultures of small numbers of CSFC or PBMC resulted in an augmentation of the number of IgSC in both, whether or not they were stimulated with PWM, and also in an increased secretion of IgG into the culture supernatants. This culture system should prove useful in functional studies when limited numbers of cells are available.

Staphylococcus aureus Cowan I. Potent stimulus of immunoglobulin M rheumatoid factor production

These studies demonstrate that Staphylococcus aureus Cowan I (SAC), a protein A-positive Staphylococcal strain, is a potent and consistent inducer of IgM rheumatoid factor production by normal human peripheral blood mononuclear cells. The frequency and magnitude of this response greatly exceeded that of parallel cultures stimulated with pokeweed mitogen or the protein A-negative S. aureus Wood strain, although all three agents induced a similar amount of total IgM. Cell fractionation studies indicated that SAC-induced IgM rheumatoid factor is T cell-dependent. The striking ability of SAC to induce IgM rheumatoid factor may relate to its protein A content, since cultures stimulated with protein A-coupled sepharose beads also consistently produced this autoantibody. Thus SAC is a new probe of in vitro IgM rheumatoid factor production and its use has provided further evidence that most healthy individuals harbor precursors of IgM rheumatoid factor secreting cells. Unlike other polyclonal activators, SAC is unique in its capacity to bind immunoglobulin, a property that may account for its prominent anti-IgG inducing capacity.

Antibodies to acetylcholine receptor and tetanus toxoid: in vitro synthesis by thymic lymphocytes

Thymic lymphocytes (TL) of patients with myasthenia gravis (MG) have been reported to synthesize antibodies to acetylcholine receptors (anti-AChR). Incubation of TL with pokeweed mitogen (PWM), a polyclonal T cell- and monocyte-dependent activator of B cell differentiation, was reported to inhibit TL in vitro synthesis of anti-AChR. We studied the TL of 16 patients with MG without thymoma. TL of 10 of 16 patients synthesized anti-AChR in vitro without stimulation. In the presence of PWM, the amount of anti-AChR synthesized by the TL of these 10 patients increased in five, decreased in three, and was unaffected in two. There was a correlation between serum anti-AChR titer and PWM-stimulated synthesis (r = 0.87), but not with unstimulated synthesis (r = 0.33) of anti-AChR by TL. There was no correlation between the amount of synthesized anti-AChR and the amount of secreted IgG or with the percentage of B cells (surface Ig+) in the TL suspensions. TL of three age-matched cardiac surgery controls failed to synthesize detectable anti-AChR, although two of three synthesized IgG. Four patients with MG were booster immunized with tetanus toxoid (TT) 3 to 4 wk prior to thymectomy. TL of three synthesized anti-TT in vitro, whereas TL of three nonboosted MG patients failed to synthesize anti-TT. Thus, we have shown that TL of some patients with MG are capable of anti-AChR synthesis, with evidence of heterogeneity of the in vitro response, and the B cell repertoire in the thymus may, in part, reflect recent systemic immune events of the host.

Antibodies to acetylcholine receptor and tetanus toxoid: in vitro synthesis by thymic lymphocytes

Thymic lymphocytes (TL) of patients with myasthenia gravis (MG) have been reported to synthesize antibodies to acetylcholine receptors (anti-AChR). Incubation of TL with pokeweed mitogen (PWM), a polyclonal T cell- and monocyte-dependent activator of B cell differentiation, was reported to inhibit TL in vitro synthesis of anti-AChR. We studied the TL of 16 patients with MG without thymoma. TL of 10 of 16 patients synthesized anti-AChR in vitro without stimulation. In the presence of PWM, the amount of anti-AChR synthesized by the TL of these 10 patients increased in five, decreased in three, and was unaffected in two. There was a correlation between serum anti-AChR titer and PWM-stimulated synthesis (r = 0.87), but not with unstimulated synthesis (r = 0.33) of anti-AChR by TL. There was no correlation between the amount of synthesized anti-AChR and the amount of secreted IgG or with the percentage of B cells (surface Ig+) in the TL suspensions. TL of three age-matched cardiac surgery controls failed to synthesize detectable anti-AChR, although two of three synthesized IgG. Four patients with MG were booster immunized with tetanus toxoid (TT) 3 to 4 wk prior to thymectomy. TL of three synthesized anti-TT in vitro, whereas TL of three nonboosted MG patients failed to synthesize anti-TT. Thus, we have shown that TL of some patients with MG are capable of anti-AChR synthesis, with evidence of heterogeneity of the in vitro response, and the B cell repertoire in the thymus may, in part, reflect recent systemic immune events of the host.

Effect of PHA-activated T cells on B-cell differentiation

Recent studies indicate that human T cells expressing the T4 determinant are comprised of functionally distinct subsets. We investigated if activation of OKT4+ cells with the mitogen PHA affected their ability to regulate the proliferation and polyclonal differentiation of autologous B cells. OKT4+ cells were preactivated with PHA and then cocultured with autologous B cells in the presence or absence of PWM. B-cell proliferation and differentiation to immunoglobulin-secreting cells (IgSC) were assessed by [3H]thymidine incorporation and reverse haemolytic plaque assay, respectively. In the absence of PWM, the PHA-activated OKT4+ cells demonstrated radioresistant help and radiosensitive suppression of IgSC responses. Addition of PWM to cocultures of irradiated PHA preactivated OKT4 cells and autologous B cells resulted in further suppression of IgSC responses, suggesting that PWM activated yet another suppression mechanism. Addition of PWM caused diminished B-cell proliferation as well. These data demonstrate functional heterogeneity within the OKT4 subset, and suggest that the particular immunoregulatory activity displayed is influenced by the state and mode of activation of these cells.

In vitro binding of an IgE protein to human platelets

Bronchoconstriction in extrinsic asthma is initiated by mediators released from IgE-sensitized leukocytes after contact with polyvalent antigen. Because platelets also contain soluble mediators that can cause bronchoconstriction, platelet activation and release of the contents of platelet granules may play a role in IgE-mediated responses under some circumstances. We therefore sought to determine if platelets are capable of binding IgE and if cross-linking this cell-bound IgE initiates secretion of platelet granule contents. Platelets from 10 normal donors were studied by using automated fluorescence analysis and fluorescence microscopy. We detected binding of a purified myeloma IgE protein to 24.1 +/- 9.6% (mean +/- 2 SD) of the gel-filtered platelets from these normal individuals. Although we could detect the binding of IgE and anti-IgE to a minority of cells, every normal individual had a population of platelets that bound IgE. The amount of IgE that bound to normal platelets appeared to be distributed heterogeneously among the IgE-positive platelet population. Platelets from two individuals with type II Glanzmann's thrombasthenia bound normal amounts of heat-aggregated IgG, but less than 3% of the platelets bound detectable IgE. Moreover, a combination of monoclonal antibodies to glycoproteins IIb and IIIa inhibited the binding of the IgE protein to normal platelets but did not affect the binding of aggregated IgG. Thus, the binding of IgE to human platelets appeared to require the presence of the glycoprotein IIb-IIIa complex. Binding of monomeric IgE to platelets, by itself, did not initiate either platelet aggregation or release of 14C-serotonin. However, both aggregation and secretion of serotonin followed the addition of anti-IgE to IgE-sensitized platelets. These studies indicate that human platelets can bind an IgE myeloma protein in vitro and that cross-linking of surface-bound IgE with anti-IgE initiates aggregation and secretion. If platelets have a similar capacity to bind normal IgE in vivo, it is possible that platelets may participate directly in several atopic or inflammatory disorders in man mediated by this class of antibody.

In vitro binding of an IgE protein to human platelets

Bronchoconstriction in extrinsic asthma is initiated by mediators released from IgE-sensitized leukocytes after contact with polyvalent antigen. Because platelets also contain soluble mediators that can cause bronchoconstriction, platelet activation and release of the contents of platelet granules may play a role in IgE-mediated responses under some circumstances. We therefore sought to determine if platelets are capable of binding IgE and if cross-linking this cell-bound IgE initiates secretion of platelet granule contents. Platelets from 10 normal donors were studied by using automated fluorescence analysis and fluorescence microscopy. We detected binding of a purified myeloma IgE protein to 24.1 +/- 9.6% (mean +/- 2 SD) of the gel-filtered platelets from these normal individuals. Although we could detect the binding of IgE and anti-IgE to a minority of cells, every normal individual had a population of platelets that bound IgE. The amount of IgE that bound to normal platelets appeared to be distributed heterogeneously among the IgE-positive platelet population. Platelets from two individuals with type II Glanzmann's thrombasthenia bound normal amounts of heat-aggregated IgG, but less than 3% of the platelets bound detectable IgE. Moreover, a combination of monoclonal antibodies to glycoproteins IIb and IIIa inhibited the binding of the IgE protein to normal platelets but did not affect the binding of aggregated IgG. Thus, the binding of IgE to human platelets appeared to require the presence of the glycoprotein IIb-IIIa complex. Binding of monomeric IgE to platelets, by itself, did not initiate either platelet aggregation or release of 14C-serotonin. However, both aggregation and secretion of serotonin followed the addition of anti-IgE to IgE-sensitized platelets. These studies indicate that human platelets can bind an IgE myeloma protein in vitro and that cross-linking of surface-bound IgE with anti-IgE initiates aggregation and secretion. If platelets have a similar capacity to bind normal IgE in vivo, it is possible that platelets may participate directly in several atopic or inflammatory disorders in man mediated by this class of antibody.