ular ▁memb rane ▁or ▁presented ▁by ▁IL - 1 5 R α ▁re ceptor . ▁ ▁The ▁main ▁mechanism ▁of ▁IL - 1 5 ▁signal ing ▁is ▁trans - presentation ▁which ▁is ▁medi ated ▁by ▁memb rane - bound ▁complex ▁IL - 1 5 / IL - 1 5 R α ▁( Fig ure ▁ 3 ). ▁IL - 1 5 ▁bind ▁to ▁IL - 1 5 R α ▁re ceptor ▁alone ▁with ▁aff inity ▁( K a ▁= ▁ 1 . 1 0 1 1 / M ). ▁It ▁can ▁also ▁bind ▁to ▁IL - 1 5 R β γ c ▁signal ing ▁complex ▁with ▁lower ▁aff inity ▁( K a ▁= ▁ 1 . 1 0 9 / M ) ▁( Fig ure ▁ 4 ). ▁ ▁Sign aling ▁path way ▁of ▁IL - 1 5 ▁begins ▁with ▁binding ▁to ▁IL - 1 5 R α ▁re ceptor , ▁with ▁subsequent ▁presentation ▁to ▁surrounding ▁cells ▁bearing ▁IL - 1 5 R β γ c ▁complex ▁on ▁their ▁cell ▁surface . ▁Upon ▁binding ▁IL - 1 5 β ▁sub unit ▁activ ates ▁Jan us ▁kin ase ▁ 1 ▁( J ak 1 ) ▁and ▁ γ c ▁sub unit ▁Jan us ▁kin ase ▁ 3 ▁( J ak 3 ), ▁which ▁leads ▁to ▁ph osph ory lation ▁and ▁activation ▁of ▁signal ▁trans du cer ▁and ▁activ ator ▁of ▁trans cription ▁ 3 ▁( STAT 3 ) ▁and ▁ST AT 5 . ▁Due ▁to ▁sharing ▁of ▁re ceptor ▁sub un its ▁between ▁IL