▁and ▁gran ul ocy te - mac roph age ▁col ony - st im ulating ▁factor ▁( GM - CS F ), ▁IL - 1 5 ▁belongs ▁to ▁the ▁four ▁α - hel ix ▁bundle ▁family ▁of ▁cy tok ines . ▁ ▁IL - 1 5 ▁is ▁const itut ively ▁expressed ▁by ▁a ▁large ▁number ▁of ▁cell ▁types ▁and ▁t issues , ▁including ▁mon ocy tes , ▁macro ph ages , ▁d end rit ic ▁cells ▁( DC ), ▁ker atin ocy tes , ▁fib ro bl asts , ▁my ocy te ▁and ▁n erve ▁cells . ▁As ▁a ▁ple iot rop ic ▁cy tok ine , ▁it ▁plays ▁an ▁important ▁role ▁in ▁inn ate ▁and ▁adapt ive ▁imm unity . ▁ ▁Gene ▁▁ ▁IL - 1 5 ▁is ▁ 1 4 - 1 5 ▁k Da ▁g ly cop rote in ▁encoded ▁by ▁the ▁ 3 4 ▁k b ▁region ▁of ▁chrom os ome ▁ 4 q 3 1 ▁in ▁humans , ▁and ▁at ▁the ▁central ▁region ▁of ▁chrom os ome ▁ 8 ▁in ▁m ice . ▁The ▁human ▁IL - 1 5 ▁gene ▁compr ises ▁nine ▁ex ons ▁( 1 ▁- ▁ 8 ▁and ▁ 4 A ) ▁and ▁eight ▁intr ons , ▁four ▁of ▁which ▁( ex ons ▁ 5 ▁through ▁ 8 ) ▁code ▁for ▁the ▁m ature ▁protein ▁( Fig ure ▁ 1 ). ▁ ▁Two ▁altern atively ▁sp lic ed ▁trans cript ▁variants ▁of ▁this ▁gene ▁encoding ▁the ▁same ▁protein ▁have ▁been ▁reported . ▁The ▁originally ▁identified