Cytokine, Chemokine, and Soluble CD14 Concentrations in the Cerebrospinal Fluid of Healthy Horses

Abstract: Background – There is growing interest in cerebrospinal fluid (CSF) biomarkers in equine neurologic disease. Biomarker interpretation requires establishment of reference ranges in healthy horses.
Hypothesis/Objectives – To establish reference ranges for twelve immune markers in CSF, and tetanus antibody (tetAb) concentrations in serum and CSF of healthy horses, including serum:CSF tetAb dilution characterization.
Animals – Forty horses from a convenience population enrolled in terminal research studies, with no evidence of neurologic disease and normal CSF cytology.
Methods – Prospective study with antemortem serum and immediate postmortem CSF collection. Cytokines (IFN-α, IFN-γ, IL-4, IL-10, IL-17), chemokines (CCL2, CCL3, CCL5, CCL11, TNF-α, IL-1β), and soluble CD14 (sCD14) were quantified using fluorescent bead-based Luminex® assays developed at the Animal Health Diagnostic Center, Cornell University. Relative tetAb concentrations were determined using a high-titer serum standard. Medians and reference intervals were calculated, effects of age, sex, and breed assessed, and CSF concentrations compared with serum.
Results – Reference ranges for detectable CSF biomarkers IL-10, CCL2, CCL11, TNF-α, and sCD14 were established. Their concentrations were not influenced by sex or breed. TNF-α CSF concentrations increased with age (rsp=0.4001, p=0.0105). IL-10, CCL11, and sCD14 concentrations were lower in CSF than in serum (p < 0.0001), whereas TNF-α concentrations were higher (p=0.0077). Serum tetAbs exceeded CSF concentrations (p < 0.0001). The median serum:CSF tetAb ratio was 367 (range 122–850).
Conclusions and Clinical Importance – Reference ranges of CSF immune markers in healthy horses provide baseline data for investigation of blood-CSF barrier integrity and biomarker identification in equine neurologic disease.