▁and ▁faster ▁response ▁to ▁second ▁and ▁up coming ▁imm une ▁challeng es . ▁ ▁Prim ing ▁of ▁na ï ve ▁T ▁cells ▁requires ▁d end rit ic ▁cell ▁ant igen ▁presentation . ▁Prim ing ▁of ▁na ive ▁CD 8 ▁T ▁cells ▁generates ▁c yt ot ox ic ▁T ▁cells ▁capable ▁of ▁directly ▁killing ▁path ogen - in fect ed ▁cells . ▁CD 4 ▁cells ▁develop ▁into ▁a ▁diverse ▁array ▁of ▁effect or ▁cell ▁types ▁depending ▁on ▁the ▁nature ▁of ▁the ▁signals ▁they ▁receive ▁during ▁prim ing . ▁CD 4 ▁effect or ▁activity ▁can ▁include ▁c yt ot ox icity , ▁but ▁more ▁frequently ▁it ▁involves ▁the ▁secret ion ▁of ▁a ▁set ▁of ▁cy tok ines ▁that ▁direct s ▁the ▁target ▁cell ▁to ▁make ▁a ▁particular ▁response . ▁This ▁activation ▁of ▁na ive ▁T ▁cell ▁is ▁controlled ▁by ▁a ▁variety ▁of ▁signals : ▁recognition ▁of ▁ant igen ▁in ▁the ▁form ▁of ▁a ▁pe pt ide : M HC ▁complex ▁on ▁the ▁surface ▁of ▁a ▁special ized ▁ant igen - present ing ▁cell ▁del ivers ▁signal ▁ 1 ; ▁interaction ▁of ▁co - st im ul atory ▁mole cules ▁on ▁ant igen - present ing ▁cells ▁with ▁re cept ors ▁on ▁T ▁cells ▁del ivers ▁signal ▁ 2 ▁( one ▁notable ▁example ▁includes ▁a ▁B 7 ▁lig and ▁complex ▁on ▁ant igen - present ing ▁cells ▁binding ▁to ▁the ▁CD 2 8 ▁re ceptor ▁on ▁T ▁cells ); ▁and ▁cy tok ines ▁that ▁control ▁different iation ▁into ▁different ▁types ▁of ▁effect or ▁cells ▁deliver ▁signal