Anti-idiotypic antibodies that inhibit immediate-type skin reactions in unsensitized monkeys on challenge with staphylococcal enterotoxin

Concomitant loss of conformation and superantigenic activity of staphylococcal enterotoxin B deletion mutant proteins

The T-cell-stimulating activity of staphylococcal enterotoxin B (SEB) is an important factor in the pathogenesis of certain staphylococcal diseases. To investigate the immunologically active domains of the SEB molecule, we have produced truncated fragments of recombinant SEB by C-terminal and N-terminal deletions. The fragments were expressed as fusion proteins with protein A, including a cleavage site to remove the protein A part. Mutant proteins were tested for the ability to stimulate human resting T cells and SEB-reactive T-cell clones. Deletion of only 9 amino acids from the C terminus leads to complete loss of T-cell-stimulating activity. Removing further amino acids from the SEB molecule did not lead to a reexpression of T-cell-mitogenic activity. A mutant protein, however, in which the 9 C-terminal amino acids were replaced with a tail of 68 amino acids encoded by the vector was fully active. Two mutant proteins with N-terminal deletions of 60 and 81 amino acids were inactive as well. A neutralizing monoclonal antibody against a conformational epitope lost binding with all the inactive mutant proteins only, whereas a monoclonal antibody recognizing an epitope involved in emetic activity reacted with all mutant proteins. These results suggest that even small deletions at the C terminus affect the three-dimensional conformation of the SEB molecule.

Monoclonal anti-idiotypic antibodies regulate the expression of virus-induced murine myocarditis

A monoclonal anti-idiotypic antibody (anti-Id), produced by electrofusion and designated anti-Id88, was able to modulate expression of murine autoimmune myocarditis mediated by coxsackievirus B3 (CVB3). The anti-Id was characterized as an immunoglobulin G2b species possessing kappa light chains and was able to reduce expression of inflammatory myocarditis in anti-Id-pretreated mice challenged with CVB3. Anti-Id88 was able to stimulate specific cell-mediated immunity against anti-Id88, as well as CVB3, and exerted a suppressive effect on the proliferation of mixed spleen cell populations from virus-exposed mice. Anti-Id stimulated an anti-anti-Id antibody 3 population able to bind antibody 2 F(ab')2 fragments or virus antigen in an indirect enzyme-linked immunosorbent assay. Western blot (immunoblot) analysis of anti-Id88 exhibited binding of syngeneic anti-Id antibody to idiotypes present on immunoglobulin G molecules from virus-immunized mice.

Mast cell activation by group A streptococcal polysaccharide in the rat and its role in experimental arthritis

Acute edematous responses were induced in Sprague-Dawley rats by the intravenous injection of group-specific polysaccharide (PS) isolated from group A streptococci. Thirty minutes after the intravenous injection of PS there was marked degranulation of subcutaneous and periarticular mast cells in all 4 feet, carbon particle labeling of adjacent venules, and an 8-fold increase in Evans blue dye content of the extremities. This acute reaction to PS was completely blocked by pretreatment with compound 48/80, but the polyarticular relapsing arthritis following the systemic injection of an arthropathic dose of streptococcal cell wall fragments containing large, covalently bound peptidoglycan-polysaccharide (PG-PS) was not blocked.

Protection against the staphylococcal enterotoxin-induced intestinal disorder in the monkey by anti-idiotypic antibodies

The staphylococcal enterotoxin serotype B (SEB)-induced enteric intoxication and the immediate-type reaction in the skin of unsensitized monkeys was used to define whether agents competing with SEB for target cell receptors may inhibit pathophysiological effects. For this purpose a duodenal provocation test was developed by use of a pediatric gastroscope, allowing the evaluation of the influence of antagonists on the intestinal disorder upon SEB challenge at the same duodenal site. First, carboxymethylation of histidine residues of SEB caused a complete loss of emetic and skin-sensitizing activity without changing the immunological specificity. However, carboxymethylated SEB is a strong inhibitor of enteric intoxications and immediate-type skin reactions upon SEB challenge. Second, after immunization of BALB/c mice with monoclonal anti-SEB antibodies, monoclonal antiidiotypic antibodies (anti-Id) were obtained by the "hybridoma technique" and purification by idiotype-affinity chromatography. Anti-Id specifically inhibited the binding of horseradish peroxidase-labeled anti-SEB to the ligand, and SEB blocked as well the interaction of these two antibody species, indicating a high degree of binding-site selectivity. Anti-Id completely protected against emetic response and diarrhea upon duodenal provocation with SEB and inhibited immediate-type skin reactions as well. Further, anti-Id acted as an antagonist without triggering biologic functions themselves. This shows that anti-Id constitute a useful tool to protect against a bacterial toxin-induced intestinal disorder.

Cysteinyl leukotrienes as mediators of staphylococcal enterotoxin B in the monkey

The role of cysteinyl leukotrienes (LTs) in the action of staphylococcal enterotoxin B (SEB) was investigated in unsensitized monkeys using inhibitors of prostanoid synthesis and LT action and by measuring generation of LT in vivo. LY 171883, a selective LTD4/LTE4 receptor antagonist, proved highly efficient in inhibiting immediate-type hypersensitivity reactions in the skin and protecting against the emetic response provoked by SEB in a concentration-dependent manner. Inhibition of prostanoid formation by pretreatment of monkeys with indomethacin or aspirin did not influence SEB responses. Based on chromatographic and radioimmunologic analysis, the generation of endogenous cysteinyl LTs was demonstrated in vivo. The concentration of LTE4, the major biliary cysteinyl LT detected, increased ten-fold and a novel cysteinyl LT metabolite in urine indicated strongly enhanced LT generation upon challenge with SEB. Cysteinyl LTs are important mediators in the pathophysiology of SEB-induced enteric intoxication. Therefore, cysteinyl LT antagonists may be of therapeutic value in the treatment of this intestinal disorder.