TNF and infection: Intracellular cytokine staining confirmed the absence of TNF production in immune populations from the brain, galea, and bone flap of TNF KO animals (Fig. 2B-D), and sham craniotomy elicited few immune infiltrates (Additional File 1: Fig. S3A-D), directly implicating infection as the cause of leukocyte recruitment, as opposed to danger-associated molecular patterns released from damaged tissues.