Using a snake toxin like a proteic antigen (Ag), two murine toxinCspecific monoclonal antibodies (mAbs), splenocytes, and two murine AgCspecific T cell hybridomas, we showed that soluble protein A (SpA) from and protein G from subspecies, two Ig binding proteins (IBPs), not only abolish the capacity of the mAbs to decrease Ag presentation but also increase Ag presentation 20C100-fold. are enriched in cells comprising SpA receptors. Fourth, the improving effect mainly diminishes when splenocytes are depleted of cells comprising SpA receptors. Fifth, the improving effect happens only when IBP simultaneously consists of a Fab and an Fc binding site. Completely, our data suggest that soluble IBPs can bridge immune complexes to APCs comprising IBP receptors, raising the possibility that during an infection process by bacteria secreting these IBPs, Ag-specific T cells may activate IBP receptorCcontaining B cells by a mechanism of intermolecular help, therefore leading to a nonspecific immune response. can improve opsonization, phagocytosis, match usage (15, 16), Ab-dependent cell-mediated cytotoxicity (17), and mitogenesis (18). Molecular properties of SpA are well recorded. It is a monomeric protein that can bind to an Ig molecule, free or bound to its Ag (19C21). SpA can bind to the Fc part of the Ab (22) through any of its five Fc binding domains, called EDABC (23, 24). It can also bind to the Fab region of an Ab via an alternative acknowledgement site (25C30) located in the VH website (31). This site is present in a large proportion of IgM, IgA, and IgG F(ab)2 that are restricted to the VHIII family in humans (32C34) and to the S107 and J606 family members in mice (35, 36). Therefore, SpA can interact with a large proportion of B cells and is therefore regarded as a B cell superantigen (37, 38). As SpA is naturally and efficiently secreted by (39C41), we investigated its possible influence on presentation of an AgCAb complex. In this study, we examined, inside a murine model, the influence of SpA on T cell demonstration of AgCAb complexes, using a snake toxin like a proteic Ag, two toxin-specific mAbs, splenocytes, and two Ag-specific T cell hybridomas. We display that SpA not only abolishes the capacity of mAbs to diminish Ag demonstration but also raises Ag demonstration by 20C100-fold. In addition, we display that (i) SpA targets AgCAb complex to a subpopulation of splenocytes comprising SpA receptors and primarily composed of B lymphocytes; (ii) APCs that possess SpA receptors are responsible for the boosting effect; (iii) the improving effect occurs only when the IBP simultaneously possesses ARID1B a Fab A-966492 and an Fc binding site; (iv) in the absence of its Ag, an Ab also undergoes a SpA-specific boosted demonstration. Completely, our observations suggest that SpA boosts Ag demonstration by bridging an immune complex to SpA receptors present at the surface of appropriate APCs. We also display that protein G from subspecies (ssp.) group C, another bacterial IBP, can also boost demonstration of AgCAb complexes. Our observations raise the probability that during an infection process by bacteria secreting these IBPs, Ag-specific T cells may activate IBP receptorCcontaining B cells A-966492 by a mechanism of intermolecular A-966492 help, therefore leading to a nonspecific immune response. Several reports suggest that these observations may also be prolonged to humans. Materials and Methods Proteins and Reagents Protein A from ssp., the IgG binding fragment BB, and protein G were purchased from ZZ was indicated and purified mainly because previously explained (49). Toxin was purified from venom (Pasteur Institute, Paris, France). Purity of the toxin was assessed by both reverse phase HPLC and isoelectric focusing. Biorex 70 and Bio-Gel P2 were from Bio-Rad Labs. The HPLC C18 column (25 cm 10 mm) was from Vydac. All solvents were from Merck and used without further purification. mAb B220, Mac pc-2, anti-CD4, and anti-CD8 were from your American Type Tradition Collection. Streptavidin-PE (SAPE) was purchased from Caltag Labs. Chemical Changes of Proteins Chemical Changes with NHSCFCC and NHSCbiotin. SpA was dialyzed over night at 4C against PBS before its changes with NHSCFCC. A-966492 52 nmol of SpA was consequently incubated for 1 h at space temp with 10 extra NHSCFCC. The reaction combination was filtered through a Sephadex G15 column (26 1.5.