Homeostasis is critically dependent on communication between the immune, endocrine and nervous systems, and also the opioid system. Opioids can affect immune processes directly through the activation of opioid receptors on leukocytes or indirectly through the stimulation of the corticosteroid and catecholamine release. Leukocytes can also synthesize and release opioid peptides, which act as analgesic factors during inflammatory process. Many data indicate that opioids are also immunomodulators, and can affect leukocyte migration, killing activity and apoptosis.

The aim of the study was to characterize the leukocytes (L) from the peripheral blood of centenarians.The study involved 39 subjects aged 100 years and older (group S – 33 females and 6 males) as well as 40 young healthy individuals aged 20–30 years (group K – 35 females and 5 males). In all of them, the quantitative and qualitative analysis of L from blood smear was performed.