The inflammatory response is indispensable for protective immunity, yet pathogens, including Sars-Cov2 coronavirus, often elicit excessive and harmful responses that may lead to a systemic inflammatory response syndrome known as sepsis. Our research group has shown that T cells contribute to the inflammatory response through CD28, a costimulatory molecule that by binding its B7.1/CD80 and B7.2/CD86 co-ligands leads to inflammatory cytokine production in a TCR-independent manner. Recently, Kaempfer's research group demonstrated that bacterial superantigen (SAgs) toxins are able to bind to both CD28 and B7 molecules and thereby to elicit an inflammatory cytokine storm. Moreover, they created short mimetic peptides of the CD28 dimer interface that, by inhibiting CD28 interaction with B7 molecules, attenuate signalling through human CD28, dampen inflammatory cytokine production and, in vivo, protect mice from toxic shock induced by bacterial superantigen toxins and from pandemic H1N1 and avian H5N1 influenza A virus infection. Starting from these evidences, the aim of the present project will be to characterize the signalling events regulating bacterial SAg-triggered inflammatory response following binding and stimulation of the human CD28/B7 costimulatory axis. The realization of the project will take advantage of a current collaboration with Prof. Kaempfer who will provide the CD28 homodimer interface mimetic peptides and on the availability in our laboratory of several Jurkat T cell lines expressing mutant forms of human CD28 in specific intracytoplasmic motifs.
The specific aims of the present project will be:
1. Identification of the signalling motifs within the intracellular domain of human CD28 responsible for its pro-inflammatory function following stimulation with bacterial SAgs.
2. Effects of CD28 homodimer interface mimetic peptides in inhibiting CD28-mediated pro-inflammatory functions in human T lymphocytes.
Bacteria-induced lethal toxic shock or sepsis, caused by the systemic production of inflammatory cytokines, is the second most common cause of death in non-coronary intensive care units and the tenth overall cause of death in high income countries. Treatment of sepsis still remains a serious concern and challenge in hospitals. Bacterial SAgs secreted by Gram-positive staphylococcal and streptococcal bacterial strains strongly contribute to sepsis by overstimulating the inflammatory response by orders of magnitude. A better understanding of the mechanisms by which bacterial SAgs modulate host defence is required for a more efficient way of targeting lethal SAg toxins challenge and better clinical outcomes. CD28 costimulatory molecule and its B7.1/CD80 and B7.2/CD28 co-ligands have been recently identified as critical SAg receptors. Indeed, binding of bacterial SAgs into the homodimer interface of CD28/B7 costimulatory complexes leads to excessive pro-inflammatory signalling. Moreover, the recent generation of mimetic peptides targeting the B7/CD28 costimulatory axis through the CD28 homodimer interface, provided a novel, host-oriented strategy for preventing lethal host inflammatory responses to infections. How intracellular CD28 signalling is controlled by bacterial SAgs and by CD28/B7 dimer interface mimetic peptides will provide biological base for understanding the mechanisms of CD28-mediated toxic shock and for attenuating lethal host inflammatory responses, while preserving the basal response required for pathogen clearance.