The main goal of this study is to investigate the impact of aging on the responsiveness of peripheral blood immune cells. To this aim, the investigators will take advantage of a recently described syringe-based assay system that can reproducibly assess induced, innate or adaptive immune responses. Briefly, a total of 50 healthy volunteers will participate to this study: 25 will be older than 18 and younger than 30, and 25 will be older than 55. A total of 14 ml of blood will be drawn including 5 X 1 ml in TruCulture™ tubes containing poly(I:C), R-848, LPS, CpG, or no stimulus, respectively. After 22 hours of incubation at 37°C, cellular supernatants will assessed for levels of 10 different chemokines using a MesoScaleDiscovery multiplexing platform.

Inclusion Criteria:

• volunteers will be invited to settle an appointment with the Nice University Hospital (CHU de Nice) Research Clinical Center (CRC).
• being between 18 and 30 year-old (group Y) or being older than 55 year-old (group O),
• ability to understand and speak French,
• being registered at the Social Security,
• acceptance to be serologically tested for HIV and HVC,
• considered healthy based on both past medical records and the clinical examination performed at the inclusion visit,
• exhibiting a body mass index (body mass divided by the square of their height) comprised between 18.5 and 30.0 kg/m2.

Exclusion Criteria:

• having participated to a drug clinical trial since less than 3 months,
• having traveled to a tropical or a sub-tropical country over the past 3 months,
• being pregnant or a lactating mother (for women),
• having performed intensive physical exercise over the past 12 hours,
• following a specific diet for medical reasons,
• over-drinking, i.e. more that 50 g of pure alcohol every day,
• having taken an immuno-suppressive or immuno-modulatory drug over the past two weeks, or for at least 14 consecutive days over the past 6 months,
• having been vaccinated over the past 3 months,
• declaring not being on an empty stomach for less than 12 hours,
• having received a blood transfusion or intravenous immunoglobulins over the past 3 months,
• declaring being HIV- or HVC- positive,
• having suffered from an infection since less than 3 weeks,
• exhibiting a positive urine pregnancy test at the inclusion visit,
• suffering from a severe/chronic/relapsing pathology, i.e. inflammatory bowel disease, psoriasis, atopic dermatitis, rheumatoid arthritis, multiple sclerosis, type I or type II diabetes, Parkinson's disease, and (p) having been diagnosed with a cancer and not being in a remitting period for less than 5 years.