Paula M. Jardieu

Inhibition of Allergic Reactions with Antibodies to IgE

Numerous clinical studies show that direct interference with the IgE response leads to a decrease or elimination of allergic symptoms. The aim of these studies was to design a therapy aimed at decreasing IgE levels in order to ameliorate atopic disease. To this end, a murine monoclonal antibody, MAE11, directed against IgE was identified, which had all the properties necessary to interfere with IgE responses, but lacked the harmful side effects of inducing receptor cross-linking. The antibody was selected on the basis of its ability to bind circulating IgE at the same site as the high-affinity receptor, thus blocking the binding of IgE to mast cells and basophils. To allow for possible chronic administration and to avoid the problems of antigenicity, MAE11 was humanized. The best of several humanized variants, version 25 (rhumAb-E25) was selected since it possessed binding affinity and biological activity comparable to MAE11. Clinical studies are underway to determine the safety and efficacy of this treatment for allergic rhinitis and asthma.

Molecular Mimicry Between Insulin and Retroviral Antigen p73: Development of Cross-Reactive Autoantibodies in Sera of NOD and C57BL/KsJ db/db Mice

Enzyme-linked immunosorbent assay (ELISA) was used to study temporal development of murine autoantibodies against insulin and both type C and intracisternal type A retroviral antigens. The nonobese diabetic (NOD) mouse, a model for autoimmune, insulin-dependent diabetes, was compared with a related, but diabetes-resistant, strain, nonobese normal (NON). Similarly, C57BL/KsJ db/db mice (insulin-resistant model of insulin-dependent diabetes and obesity) were compared with diabetes-resistant C57BL/6 db/db mice. NOD mice developed much higher autoantibody titers than did NON mice. Whereas type C autoantibodies in NOD developed to peak titer shortly after mice were weaned, autoantibodies against insulin and p73 (group-specific antigen of the intracisternal type A particle) did not develop until shortly before, or concomitant with, the development of hyperglycemia. Two NOD mice not developing hyperglycemia during the 40-wk study period were distinguished from the mice developing diabetes by a delayed onset of insulin (but not p73) autoantibodies. Our findings suggest that in NOD mice, the appearance of insulin and p73 autoantibodies signifies that extensive underlying necrosis of β-cells occurred. C57BL/KsJ db/db mice (with extensive β-cell necrosis and early hyperglycemia) developed much higher autoantibody titers to insulin and p73 than did the diabetes-resistant C57BL/6 db/db mice. However, the presence of autoantibodies in normoglycemic C57BL/KsJ +/db controls demonstrated that elevated autoantibody titers alone were insufficient to produce diabetes in this model. Absorption studies indicated that autoantibodies against p73 recognized a common epitope on insulin and IgE-binding factor. The potential significance of this molecular mimicry is discussed.

T Cell Factors Involved in the Regulation of the IgE Synthesis

The IgE-potentiating and IgE-suppressive factors share a common structural gene and therefore a common polypeptide chain, and their biologic activities are decided by a post-translational glycosylation process. Under physiological conditions, this process is controlled by two T cell factors, i.e., the glycosylation-enhancing factor (GEF) and glycosylation-inhibiting factor (GIF). GIF is a fragment of phosphorylated lipocortin and has immunosuppressive effects. Repeated injections of this lymphokine into antigen-primed mice switched their T cells from the formation of IgE-potentiating factor to the formation of IgE-suppressive factor and facilitated the generation of antigen-specific suppressor T cells, which form antigen-specific GIF upon antigenic stimulation. The antigen-specific GIF suppressed the antibody response in a carrier-specific manner and has properties similar to antigen-specific suppressor T cell factors.

Role of Glycosylation Inhibiting Factor (GIF), a Phospholipase Inhibitory Protein, in the Generation of Antigen-Specific Suppressor T Cells

Previous experiments on the isotype-specific regulation of the IgE antibody response revealed T cell factors which have affinity for IgE and either enhance or suppress the IgE response (1). The major differences between the IgE-potentiating factors (PF) and IgE-suppressive factors (SF) are carbohydrate moieties in the molecules. The IgE-potentiating factors bind to lentil lectin and Con A, suggesting that the factors contain N-linked, mannose-rich oligosaccharide. In contrast, IgE-suppressive factors have no affinity for these lectins but bound to peanut agglutinin (2). Recent experiments in collaboration with Drs. Moore and Martens in DNAX Institute of Molecular Biology indicate that IgE-PF and IgE-SF share a common structural gene (3). Transfection of COS 7 monkey kidney cells with the cDNA clone 8.3, which encodes the rodent IgE-binding factor (4) resulted in the formation of IgE-PF, whereas the transfection of the same cells with the same cDNA clone in the presence of tunicamycin resulted in the formation of IgE-SF.

Cloning of an IgE Immunoregulatory Factor by Expression in Mammalian Cells

T lymphocytes and their products regulate synthesis of immunoglobulin by B lymphocytes at several levels. T-cells may help or suppress immune responses in an antigen-specific or non-specific way, or may regulate idiotype or isotype-specific responses. Several researchers have described isotype specific regulation of the synthesis of IgE, IgA, and IgG in rodents as well as humans. Certain characteristics appear to be common to such regulation: the T cells which regulate the synthesis of a heavy-chain isotype by B-cells bear Fc receptors specific for that isotype and these Fc receptor-bearing lymphocytes secrete factors which are active in regulating immunoglobulin synthesis by B-cells. In general, the soluble factors bind specifically to the Fc region of the immunoglobulin isotype which they regulate, and appear to be related structurally to the lymphocyte Fc receptor. We refer to this family of isotype-specific regulatory factors as “immunoglobulin-binding factors”, or Ig-BF.