Detection of interleukin-1 bioactivity in various brain regions of normal healthy rats

Although interleukin-1 (IL-1) has been implicated in an array of brain functions, past studies usually have failed to detect IL-1 bioactivity in the brain of normal healthy animals. However, in view of the potency of IL-1 in brain, small amounts of this cytokine may normally act in brain, and such quantities can escape detection by assay methods usually employed. Although bioassays are highly sensitive for detecting IL-1, these can be compromised by molecules in brain tissue other than IL-1, and attempts to purify IL-1 from brain tissue can result in significant loss of IL-1 from samples. In this study, we have refined our method of assessing brain IL-1 bioactivity by first semi-isolating IL-1 with a Sephadex minicolumn and then measuring IL-1 activity with a sensitive D10 cell assay. To confirm that our assay was specific for IL-1, a monoclonal antibody against IL-1 receptor was used to block any observed IL-1 activity. We report here that IL-1 bioactivity can be reliably detected in both the cell-free supernatant and cell lysate of brainstem, cortex, diencephalon, and hippocampus of normal rat brain. These results lend support to some recent studies that found IL-1 may play important roles in the functions of normal brain.