CCAAT/enhancer-binding protein δ (C/EBPδ) aggravates inflammation and bacterial dissemination during pneumococcal meningitis

Abstract

Background: The prognosis of bacterial meningitis largely depends on the severity of the inflammatory response. The transcription factor CAAT/enhancer-binding protein δ (C/EBPδ) plays a key role in the regulation of the inflammatory response during bacterial infections. Consequently, we assessed the role of C/EBPδ during experimental meningitis.

Methods: Wild-type and C/EBPδ-deficient mice (C/EBPδ(-/-)) were intracisternally infected with Streptococcus pneumoniae and sacrificed after 6 or 30 h, or followed in a survival study.

Results: In comparison to wild-type mice, C/EBPδ(-/-) mice showed decreased bacterial loads at the primary site of infection and decreased bacterial dissemination to lung and spleen 30 h after inoculation. Expression levels of the inflammatory mediators IL-10 and KC were lower in C/EBPδ(-/-) brain homogenates, whereas IL-6, TNF-α, IL-1β, and MIP-2 levels were not significantly different between the two genotypes. Moreover, C/EBPδ(-/-) mice demonstrated an attenuated systemic response as reflected by lower IL-10, IL-6, KC, and MIP-2 plasma levels. No differences in clinical symptoms or in survival were observed between wild-type and C/EBPδ(-/-) mice.

Conclusion: C/EBPδ in the brain drives the inflammatory response and contributes to bacterial dissemination during pneumococcal meningitis. C/EBPδ does, however, not affect clinical parameters of the disease and does not confer a survival benefit.

Figure 1

Pneumococcal meningitis induces C/EBPδ expression. c/ebpδ mRNA (A) and protein expression in wild-type brain tissue (B, C, D) at different time points after intracisternal inoculation with S. pneumoniae. Arrows indicate epithelial cells expressing C/EBPδ in vessels of the brain parenchyma (BP) and meningeal cells. Arrowheads indicate glial cells in brain parenchyma expressing C/EBPδ (BP). Asterisk indicate C/EBPδ positive cells in the choroid plexus (CP). Original magnification ×10, inset ×20. Data are expressed as median with interquartile ranges and 5% to 95% percentiles (n = 6 for controls; n = 12 at both t = 6 and t = 30 h post infection). **P < 0.01.

Figure 2

C/EBPδ^−/− mice have less bacterial outgrowth in brain, lung, and spleen at 30 h after pneumococcal meningitis. Bacterial outgrowth in CSF and brain homogenates (A), whole blood (B), lung homogenates and spleen homogenates (C) of wild-type (open boxes) and C/EBPδ^−/− (gray boxes) 6 and 30 h after infection. Data are expressed as median with interquartile ranges and 5% to 95% percentiles (n = 12 per group). **P < 0.01 compared to wild-type mice.

Figure 3

C/EBPδ deficiency modifies the inflammatory response during pneumococcal meningitis. Cytokine (A, B, C, D) and chemokine (E, F) levels in brain homogenates and plasma of wild-type (open boxes) and C/EBPδ^−/− (gray boxes) mice 6 and 30 h after infection. Data are expressed as median with interquartile ranges and 5% to 95% percentiles (n = 11 to 12 per group). *P < 0.05 compared to wild-type control mice.

Figure 4

Effect of C/EBPδ deficiency on the clinical status during pneumococcal meningitis. Clinical scores of wild-type and C/EBPδ^−/− mice at different time points during meningitis. A.U. = arbitrary units; dashed line indicates the maximal score of 15.

Figure 5

Effect of C/EBPδ deficiency on organ damage during pneumococcal meningitis. Levels of general tissue injury marker lactate dehydrogenase (LDH; A), liver injury markers alanine transaminase (ALAT; B) and aspartate transaminase (ASAT; C) in plasma of wild-type (open boxes) and C/EBPδ^−/− (gray boxes) 30 h after infection. Data are expressed as median with interquartile ranges and 5% to 95% percentiles. *P < 0.05 compared to wild-type control mice.

Figure 6

Effect of C/EBPδ deficiency on blood-brain barrier status and survival. Brain/plasma albumin ratio in wild-type (open boxes) and C/EBPδ^−/− (gray boxes) 30 h after infection. Data are expressed as median with interquartile ranges and 5% to 95% percentiles. *P < 0.05 compared to wild-type control mice (A). Survival of wild-type (black circle) and C/EBPδ^−/− mice (black square) after induction of pneumococcal meningitis (n = 12 mice per group; B).