Cerebrospinal fluid levels of soluble CD14 in inflammatory and non-inflammatory diseases of the CNS: upregulation during bacterial infections and viral meningitis.

The CD14 antigen, an important cell surface molecule of monocytic cells, is involved in cellular activation: it binds lipopolysaccharide and other cellular lipid structures. Brain macrophages play a pivotal role during inflammatory reactions of the CNS parenchyma, ventricles and meninges. A soluble form of CD14 (sCD14) was measured in paired cerebrospinal fluid (CSF) and serum samples from 91 patients with different neurological diseases. Mean levels of circulating sCD14 in CSF in a control group of 22 patients with neurologic complaints but no neurological deficit on clinical examination were 0.19 +/- 0.06 (mean +/- SD) mg/l. The CSF/blood ratios of sCD14 was 49 +/- 16 x 10(-3), while those of albumin were 4.4 +/- 1.4 x 10(-3). These extremely high CSF/blood ratios of the sCD14 molecule compared to albumin indicate a local cerebral production. No significant changes in CSF sCD14 levels were found in patients with non-inflammatory neurological diseases (NID). In contrast, CSF sCD14 levels were markedly elevated during acute meningitis, but there was no direct correlation between sCD14 and monocyte count in the CSF. Thus, sCD14 could not originate in the CSF compartment from monocytes alone. The highest values for sCD14 were found in CSF during infections with various pathogens such as Staphylococcus aureus or Listeria monocytogenes. While sCD14 serum levels dramatically increased during acute bacterial meningitis, sCD14 ratios did not correlate with albumin ratios during the course of disease. Therefore, increased CSF sCD14 may originate from cerebral production by activated or infiltrated macrophages rather than passive diffusion from the blood, while elevated sCD14 serum levels resulted from enhanced local production. Increased CSF and serum sCD14 values were also observed in meningitis caused by viral infection. As in bacterial meningitis, sCD14 in CSF specimens did not correlate with the function of the blood/CSF barrier. Repeated lumbar punctures revealed a normalization of CSF sCD14 levels during clinical recovery. These results provide the first evidence for local production of sCD14 within the CNS. Our findings further indicate that sCD14 in CSF is a reliable marker for activation of macrophages within the CNS during inflammatory processes.