    Sentence 1: What is the complex “two-signal” activation  ‘of T cells referred to?    ‘Sentence 2: On the basis of CST, Burnet developed a theory  ‘of Kow an inimune response is triggered: according to the  Sec fanehoe ar ee een Coainta  fur bnign a nek oye: duscuces inane eaponaes  while “noriselt” entities (pathoge! gga ft trigger  Yestucireimnane rorponse, beg?