A teenаge mаle is diаgnоsed with multiple trauma and a clоsed head injury fоllowing a motor vehicle accident. His initial lab work is as follows: WBC 13,000 Segs Normal RBC 3.0 Bands Increased Hgb 6 Eosinophils Normal Hct 18% Basophils Normal Plt 180,000 Lymphocytes Increased Monocytes Normal Based on the above lab work, which of the following is the most likely cause of the increased white blood cells?