Severe infections (sepsis) are a common cause of admission to the intensive care unit. They represent a significant health risk for patients in the short and medium term. They are particularly linked to a change in the function of immune cells. In some patients, a state of pseudo-dormancy of monocyte and macrophage-type immune cells, called immunosuppression of myeloid cells, is observed. This situation leads to a worsening of the infection, so it should be avoided because it represents a danger for the patient even when they ar receiving antibiotics. At present, these events are still very poorly understood. Research is essential to understand how this state of immunosuppression of myeloid cells is established in order to adapt existing treatments or find new ones.

Laboratory studies on animal models of septicaemia have shown that this state of immunosuppression of myeloid cells is closely linked to a change in the production of energy by myeloid cells (monocytes and macrophages). The functioning of the mitochondria ("energy factory" of the cells) in these cells is impaired. Thus, restoring mitochondrial function in myeloid cells could be a therapeutic solution against the immunosuppression of myeloid cells during severe septicaemia.

The objective of this study is to verify whether alterations in mitochondrial function in myeloid cells also occur in patients with bacterial infection compared to patients without bacterial infection.

Inclusion Criteria:

• Adult person who has given written consent (or consent obtained from a heath care proxy) hospitalized in an ICU with or without sepsis (with or without infection)

Exclusion Criteria:

• Person not affiliated or not benefiting from national health insurance
• Person under legal protection (curatorship, guardianship, safeguard of justice)
• Pregnant, parturient or breastfeeding woman
• Patient who was hospitalized within 3 months prior to inclusion for sepsis.
• Patients receiving known treatment for mitochondrial function modulation, mitochondrial biogenesis or mitophagy (chloroquine, hydroxychloroquine, rapamycin, carbamazepine, resveratrol, sildenafil).

Adult patients hospitalized in the ICU with or without sepsis.