The homodimer interfaces of costimulatory receptors B7 and CD28 control their engagement and pro-inflammatory signaling

Abstract

Background The inflammatory response is indispensable for protective immunity, yet microbial pathogens often trigger an excessive response, ‘cytokine storm’, harmful to the host. Full T-cell activation requires interaction of costimulatory receptors B7-1(CD80) and B7-2(CD86) expressed on antigen-presenting cells with CD28 expressed on the T cells. We created short peptide mimetics of the homodimer interfaces of the B7 and CD28 receptors and examined their ability to attenuate B7/CD28 coligand engagement and signaling through CD28 for inflammatory cytokine induction in human immune cells, and to protect from lethal toxic shock in vivo. Methods Short B7 and CD28 receptor dimer interface mimetic peptides were synthesized and tested for their ability to attenuate the inflammatory cytokine response of human peripheral blood mononuclear cells, as well as for their ability to attenuate B7/CD28 intercellular receptor engagement. Mice were used to test the ability of such peptides to protect from lethal superantigen toxin challenge when administered in molar doses far below the toxin dose. Results B7 and CD28 homodimer interfaces are remote from the coligand binding sites, yet our finding is that by binding back into the receptor dimer interfaces, short dimer interface mimetic peptides inhibit intercellular B7-2/CD28 as well as the tighter B7-1/CD28 engagement, attenuating thereby pro-inflammatory signaling. B7 mimetic peptides exhibit tight selectivity for the cognate receptor in inhibiting intercellular receptor engagement with CD28, yet each diminishes signaling through CD28. In a prominent example of inflammatory cytokine storm, by attenuating formation of the B7/CD28 costimulatory axis, B7-1 and CD28 dimer interface mimetic peptides protect mice from lethal toxic shock induced by a bacterial superantigen even when administered in doses far submolar to the superantigen. Conclusions Our results reveal that the B7 and CD28 homodimer interfaces each control B7/CD28 costimulatory receptor engagement and highlight the protective potential against cytokine storm of attenuating, yet not ablating, pro-inflammatory signaling via these receptor domains.

Targeting staphylococcal enterotoxin B binding to CD28 as a new strategy for dampening superantigen-mediated intestinal epithelial barrier dysfunctions

“…Indeed, they identified a 12 amino-acid β-strand (8)/hinge/α-helix ( 4 ) conserved region in staphylococcal SAgs that, by engaging the dimer interface of CD28 and B7, enhances their interaction triggering the cytokine storm ( 16 , 18 , 19 ). Furthermore, they also showed that short mimetic peptides targeting the homodimer interface of CD28 were able to attenuate inflammatory cytokine production by interfering with CD28/B7 engagement and signalling induced by SEB ( 16 , 17 , 19 , 22 , 97 , 98 ). More recently, we demonstrated that SEB is able to elicit massive cytokine production by engaging the TCR and CD28 in a bivalent manner and in the absence of APCs expressing B7 molecules ( 22 ).…”

“…Furthermore, they also showed that short mimetic peptides targeting the homodimer interface of CD28 were able to attenuate inflammatory cytokine production by interfering with CD28/B7 engagement and signalling induced by SEB ( 16 , 17 , 19 , 22 , 97 , 98 ). More recently, we demonstrated that SEB is able to elicit massive cytokine production by engaging the TCR and CD28 in a bivalent manner and in the absence of APCs expressing B7 molecules ( 22 ). By using the cryo-EM structure of SEB-MHCII-TCR-CD3 complex ( 99 ) and CD28 ( 38 , 100 ) together with the previously published spatial-restrained protein-protein docking approach ( 39 , 101 , 102 ), we were able to define that SEB may bind the TCR and CD28 simultaneously by adopting a wedge-like conformation ( 23 ).…”

“…The inflammatory activity of SEB depends on its capability to stimulate T cells by engaging specific TCRVb chain elements and the CD28/B7 costimulatory axis either in the presence or absence of MHC-II molecules on APCs (16)(17)(18)(19)(20)(21)(22). In particular, extensive studies from Kaempfer and co-workers pointed out a crucial role of CD28 and its co-ligand B7 in binding SEB and in stimulating T cells to produce inflammatory cytokines.…”

“…SEs may act as superantigens (SAgs) and activate a large population of T lymphocytes to produce inflammatory cytokines (13). In particular, SEB directly activate T cells bearing TCRVb3, 12, 13.2, 14, 17 and 20 (14), widely expressed in the human population (15), and CD28 costimulatory molecules either in the presence or absence of the major histocompatibility complex class II (MHC-II) or B7.1/CD80 and B7.2/CD86 molecules on antigen presenting cells (APCs) (16)(17)(18)(19)(20)(21)(22)(23). Indeed, we recently highlighted that both SEB and SEA can directly bind the TCR and CD28, activating inflammatory signalling in the absence of APCs expressing B7 and/or MHC-II (23).…”