<P> Antigen presenting cells present antigens in the form of peptides on histocompatibility molecules . The T cell / T lymphocyte ( a subtype of white blood cell ) , of the adaptive immune system , selectively recognize the antigens . Depending on the antigen and the type of the histocompatibility molecule , different types of T cells will be activated . For T - Cell Receptor ( TCR ) recognition , the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex ( MHC ) . The antigen can not elicit the immune response without the help of an immunologic adjuvant . Similarly , the adjuvant component of vaccines plays an essential role in the activation of the innate immune system . </P>
recognition proteins are used by white blood cells for what purpose
activation of the innate immune system