passages.id: split_4_test_1036_passage
passages.type: progene_text
passages.text: Using this system , we have addressed two unresolved issues : the half - life of naive CD4 ( + ) T cells in the absence of class II molecules ( 3 - 4 wk ) and the early signaling events associated with class II molecule engagement by naive CD4 ( + ) T cells ( partial CD3 zeta chain phosphorylation and ZAP - 70 association ) .