Astrocytes produce and release interleukin-1, interleukin-6, tumor necrosis factor alpha and interferon-gamma following traumatic and metabolic injury

The brain is no longer considered immune-privileged due to its capability of producing cytokines in response to neurotrauma; however, the cellular sources of cytokines have not been defined. This study focused on the production of four inflammatory cytokines, interleukin-1 (IL-1α), interleukin-6 (IL-6), tumor necrosis factor alpha (TNFα), and interferon gamma (IFN-γ) in primary culture of astrocytes under two different injury models which simulated in vivo mechanical trauma (scratch injury) and ischemia. Results demonstrated that astrocytes after scratch injury were positively immunostained with IL-1α, IL-6, and TNFα. A slot-blot study of culture media showed that the release of IL-1α, IL-6, TNFα, and IFN-γ by astrocytes subsequent to scratch and ischemic injury reached approximately twice the control values. The temporal expression of these cytokines was different for the two models. All four cytokines began to increase 1 h postscratch and remained at high levels throughout the experiment. In the ischemic model, however, the increase of cytokine expression was delayed until 4-8 h of ischemia, when sharp increases were seen in all four cytokines. In this culture system, the exogenous influence of blood-borne factors and leukocytes, which occur with in vivo trauma and ischemia, was eliminated. Accordingly, the cytokines detected in the culture media were derived from astrocytes. This study provides the first evidence that astrocytes, without the influence from other cell types, can produce and release cytokines following mechanical and ischemic injury.