Disclosed are methods and compositions for the inhibition of modulation of
T cell costimulatory pathway by a pathogenic agent, particularly, the inhibition of activation of a
T cell costimulatory pathway, preferably, the CD28 / B7 pathway, by a pyrogenic
exotoxin. The method of the invention is based on the inhibition of the direct interaction of a
superantigen with a specific site within the
dimer interface of a CD28 family member, using immunomodulatory peptides. Further disclosed are specific
antagonist immunomodulatory peptides comprising an
amino acid sequence derived from a
dimer interface of a
T cell co-stimulatory pathway member, or peptides which comprise an
amino acid sequence which specifically binds to an
amino acid sequence within the
dimer interface of a T
cell co-stimulatory pathway member. Compositions comprising said peptides and methods for the treatment of immune-related disorders are also disclosed. Also disclosed is the use of the CD28 molecule or any fragment thereof comprising the sAg
binding site in a method of screening for a test substance which specifically binds to the CD28 molecule and is capable of antagonizing pyrogenic
exotoxin-mediated activation of Th1 lymphocytes.