Memory cell in immune system are long lived and escape apoptosis because of:

D i.e. Nerve growth factorNerve growth factor inhibits apoptosis in memory B cellsQ inactivation of p38 MAPK, prevention of antiapoptotic factor Bcl-2 phosphorylation (i.e. maintaining its integrity) & cytochrome c releaseAlthough other growth factors like FGF, PDGF and IGF can also prolong the survival, it is the nerve growth factor that is most impoant in immoalization of memory cells.Growth factor --> activate P13 kinase --> activate Akt --> inactivates procaspase 9 & inhibit Fast synthesis