The initiation and early development of autoimmune diseases

Molecular mimicry and clonal deletion: A fresh look

In this article, I trace the historic background of clonal deletion and molecular mimicry, two major pillars underlying our present understanding of autoimmunity and autoimmune disease. Clonal deletion originated as a critical element of the clonal selection theory of antibody formation in order to explain tolerance of self. If we did have complete clonal deletion, there would be major voids, the infamous "black holes", in our immune repertoire. For comprehensive, protective adaptive immunity, full deletion is necessarily a rare event. Molecular mimicry, the sharing of epitopes among self and non-self antigens, is extraordinary common and provides the evidence that complete deletion of self-reactive clones is rare. If molecular mimicry were not common, protective adaptive immunity could not be all-encompassing. By taking a fresh look at these two processes together we can envision their evolutionary basis and understand the need for regulatory devices to prevent molecular mimicry from progressing to autoimmune disease.

Recognition of self and altered self by T cells in autoimmunity and allergy

T cell recognition of foreign peptide antigen and tolerance to self peptides is key to the proper function of the immune system. Usually, in the thymus T cells that recognize self MHC + self peptides are deleted and those with the potential to recognize self MHC + foreign peptides are selected to mature. However there are exceptions to these rules. Autoimmunity and allergy are two of the most common immune diseases that can be related to recognition of self. Many genes work together to lead to autoimmunity. Of those, particular MHC alleles are the most strongly associated, reflecting the key importance of MHC presentation of self peptides in autoimmunity. T cells specific for combinations of self MHC and self peptides may escape thymus deletion, and thus be able to drive autoimmunity, for several reasons: the relevant self peptide may be presented at low abundance in the thymus but at high level in particular peripheral tissues; the relevant self peptide may bind to MHC in an unusual register, not present in the thymus but apparent elsewhere; finally the relevant self peptide may be post translationally modified in a tissue specific fashion. In some types of allergy, the peptide + MHC combination may also be fully derived from self. However the combination in question may be modified by the presence of other ligands, such as small drug molecules or metal ions. Thus these types of allergies may act like the post translationally modified peptides involved some types of autoimmunity.

Celiac disease-associated autoimmune endocrinopathies

Celiac disease (CD) is an autoimmune disorder induced by gluten intake in genetically susceptible individuals. It is characterized by the presence of serum antibodies to endomysium, reticulin, gliadin, and tissue transglutaminase. The incidence of CD in various autoimmune disorders is increased 10- to 30-fold in comparison to the general population, although in many cases CD is clinically asymptomatic or silent. The identification of such cases with CD is important since it may help in the control of type I diabetes or endocrine functions in general, as well as in the prevention of long-term complications of CD, such as lymphoma. It is believed that CD may predispose an individual to other autoimmune disorders such as type I diabetes, autoimmune thyroid, and other endocrine diseases and that gluten may be a possible trigger. The onset of type I diabetes at an early age in patients with CD, compared to non-CD, and the prevention or delay in onset of diabetes by gluten-free diet in genetically predisposed individuals substantiates this antigen trigger hypothesis. Early identification of CD patients in highly susceptible population may result in the treatment of subclinical CD and improved control of associated disorders.

Synovial fluid antigen-presenting cell function in rheumatoid arthritis

We have previously demonstrated enhanced synovial fluid (SF) antigen-presenting cell (APC) function in inflammatory arthritis patients selected on the basis of marked SF mononuclear cell (MNC) responsiveness to reactive arthritis-associated bacteria (Clin Exp Immunol 1990; 79:189-94). In this study we have assessed whether similarly enhanced synovial APC function is present in other inflammatory arthritis patients by using two assay systems to study 18 rheumatoid arthritis patients whose MNC responsiveness had not been determined in advance. We demonstrate that rheumatoid SF APC are much more potent than peripheral blood (PB) APC in stimulating the responses of autologous PB T cells to a range of recall antigens. In addition, SF APC are shown to be efficient stimulators of the antigen-specific responses of MHC-compatible, cloned T cells. Enhanced synovial APC function is thus likely to be a general feature of inflammatory arthritis and may play an important role in its pathogenesis.

The onset of nephritis in the (NZB × SWR)F1 murine model for systemic lupus erythematosus correlates with an increase in the ratio of CD4 to CD8 T lymphocytes specific for the nephritogenic idiotype (IdLNF1)

An idiotypically related family of nephritogenic antibodies (IdLNF1) has been shown to be important in the pathogenesis of autoimmune glomerulonephritis in the (NZB x SWR)F1 hybrid, SNF1. Idiotype-specific T lymphocytes which modulate expression of antibody bearing that idiotype may be important in the pathogenesis of systemic lupus erythematosus (SLE). Here, IdLNF1-reactive T lymphocytes were not only found to be present in the NZB, SWR, and SNF1, but a significantly (P < or = 0.05) greater number of IdLNF1-reactive Thy 1.2+ splenic lymphocytes were observed as early as 12 weeks of age in the SNF1. Further, a significant shift in the ratio of CD4+ to CD8+ IdLNF1-reactive T lymphocytes in favor of CD4+ IdLNF1-reactive T cells was observed at 20 to 24 weeks of age only in the SNF1. This shift correlated with an increase in IdLNF1+IgG, and deposition of IdLNF1 bearing immunoglobulin in the kidney glomeruli. These observations suggest a role for idiotype-specific T lymphocytes in the induction of glomerulonephritis in this murine model of SLE.

Target organ susceptibility and autoantibody production in an animal model of spontaneous autoimmune thyroiditis

F1-hybrids of Obese strain (OS) chickens, afflicted with spontaneous autoimmune thyroiditis (SAT), and normal, inbred CB chickens, do not develop severe thyroiditis. About 50% of these crosses show circulating autoantibodies to thyroglobulin (TgAAb), but the thyroid glands are only slightly infiltrated, suggesting that the target organ is not susceptible to autoimmune attack. In the present study we show that despite this mild infiltration TgAAb are only synthesized by lymphoid cells within the thyroid gland. Furthermore, we demonstrate that immunization with chicken thyroglobulin (Tg) in complete Freund's adjuvant causes severe experimental autoimmune thyroiditis (EAT) in F1(OSxCB) hybrids.

Strategies for exploiting the immune system in the design of vaccines

There are three types of vaccines in medical use today--live, attenuated agents, mainly viruses; inactivated whole organisms; and subunit preparations. Though there are examples in each category of successful preparations, live attenuated viruses have almost invariably given long-lasting immunity after one or two administrations. Contributing reasons for this are gleaned, not from human vaccine studies, but from model systems and it is concluded that a vaccine needs to achieve four goals: activation of antigen-presenting cells; overcoming genetic variability in T cell responses; generation of high levels of T and B memory cells; and persistence of antigen for recruitment of B memory cells. Of the newer approaches to vaccine development, synthetic peptides have substantial limitations but should be successful in some cases. Subunit preparations may also be limited as a general method. Some live viral or bacterial vaccines, used as vectors of nucleic acid coding for other antigens, hold considerable promise as is illustrated by recent examples.

The concept of anti-idiotypic regulation of selected autoimmune diseases by intravenous immunoglobulin

Evidence that physiological control of human humoral autoimmune reactions depends, at least in part, on the formation of anti-idiotypic antibodies is accumulating. Upon binding to the corresponding idiotypes, anti-idiotypes will prevent autoantibodies from reacting with the primary antigen and/or eventually expedite removal of autoantibodies from the circulation and down-regulate their formation. In patients with autoantibodies against clotting factor VIII:C or fibrinogen, clinical improvement was associated with formation of anti-idiotypes against the autoantibodies. In addition, iv immunoglobulin (IVIg) preparations derived from plasma pools of thousands of healthy donors expressed anti-idiotypes against such autoantibodies as anti-clotting factor VIII:C, antithyroglobulin, and anti-intrinsic factor, but the specificity of the anti-idiotypes appears to be restricted for particular idiotypes. This explains why not all patients are responders to therapeutic intervention with IVIg. On one hand, definite in vitro neutralization of autoantibody activity by IVIg added in multiple proportions is not followed infallibly by in vivo response, and on the other hand, a good therapeutic effect often lasts long beyond normal half-lives of infused IVIg. The present overview compares the authors' own work with that described in recently published literature on exploring anti-idiotypy in therapy.

Pathogenic mechanisms in autoimmune diseases

Autoimmunity may be initiated by a variety of mechanisms involving changes in autologous antigens or alterations in immune regulation. Autoimmune disease, the pathological consequence of an autoimmune response, depends principally upon the stimulation of helper/inducer T cells reactive with self-antigens. Such T cells direct the quantity and quality of the immune response by influencing the mixture of interleukins produced. Autoantibodies react with accessible cells and mediate injury directly or indirectly. Delayed hypersensitivity reactions indirectly damage tissues through the agency of lymphokines. Cytotoxic T cells penetrate tissue spaces and attack cells bearing requisite surface antigens complexed with the appropriate major histocompatibility complex product. Macrophages and NK cells, activated by lymphokines, have potential to augment tissue damage. These several mechanisms do not operate in isolation; rather, multiple processes act in unison in most autoimmune diseases.