 They circulate in bloodstream for about 6 to 10 hours after leaving bone marrow, whereupon they undergo spontaneous apoptosis.Microbial pathogens have been reported to influence cellular apoptosis by different strategies.Obviously because of the inhibition of caspase3-activation, "L. major" can induce the delay of neutrophils apoptosis and extend their lifespan for at least 2–3 days.