post-traumatic osteomyelitis group (POM), the participants who developed post-traumatic osteomyelitis after primary surgical treatment and were taken blood sample on admission (ADD), first postoperative day (POD1) and fourth postoperative day (POD4). Patients were included in POM group after additional assessment of meeting the CDC/NHSN surveillance definition criteria for osteomyelitis: positive intraoperative withdrawal bone and soft tissue sample, types of cultured bacteria, histopathologic proof of osteomyelitis and clinical signs of surgical site infection.

No POM group, the participants who did not develop postraumatic osteomyelitis to tibia after primary surgical treatment and were taken blood sample on admission (ADD), first postoperative day (POD1) and fourth postoperative day (POD4) in follow up interval of 6 months /control group/. Patients were included in No POM group after assessment of not meeting the CDC/NHSN surveillance definition criteria for osteomyelitis.

Laboratory analyses of peripheral venous blood on admission (blood sample ADD), 24 hours after surgery (blood sample POD1) and fourth-day after surgery (blood sample POD4) included biochemical analysis, complete blood count, C-reactive protein (CPR), procalcitonin (PCT), albumin/protein level, prothrombin time and international normalized ratio (INR) (only on admission) and for determination of cytokines: tumor necrosis factor alpha (TFN-α), interleukin-6 (IL-6), interleukin-10 (IL-10).

WBC count (reference range 4-10 x 109/L), WBC differential (neutrophil count 1.50-7.40 x 109/L, lymphocyte count 1.10-3.50 x 109/L) and hematocrit (reference range 0.390-0.500) were analyzed with a hematological blood analyzer LH75 (Beckman Coulter). The immunocytochemic analyzer Modular Analytics SWE (Roche Diagnostics) was used for serum samples analysis. The serum concentration of CRP (reference range 0-5mg/L) was measured by the immunoturbidimetric method, PCT (reference range 0-0.5μg/L) by the electrochemiluminescence method and albumins (reference range 35-52g/L) by the bromcresol green method.

Whole venous blood was collected into vacutainer tubes containing EDTA. Samples were processed for flow cytometry. For surface staining, the standard whole-blood staining methodology as prescribed by the manufacturer (BDBiosciences) was used. For detecting regulatory T cells, samples were stained for surface antigens with a mix of anti-CD25-PE/ anti-CD127-APC/ anti-CD4-PE-Cy™7. All antibodies were obtained from BDBiosciences (Mountain View, Ca, USA). Cells were analyzed on FACSCantoII™ Flow Cytometer (BDBiosciences) equipped with blue (488-nm solid-state) and red (633-nm helium-neon) laser. Digital data was acquired with FACSDiva software (BDBiosciences) and analyzed using FlowJo software (Tree Star Inc.,).

Cytokine concentrations were measured by commercially available enzyme-linked immunosorbent assay (ELISA) kits. TNF-α (Milenia Biotec, Germany), IL-6 and IL-10 (Thermo Scientific, USA) were measured according to the manufacturer's instructions.