The effects of irradiation on cytokine production in glioma cell lines, NP1, NP2 and NP3, were studied. Culture supernatants were collected after 6, 24, 48 or 72 hours and the concentrations of interleukin (IL)-6 and IL-8 measured by enzyme-linked immunosorbent assay. Spontaneous and IL-1β-stimulated productions were analyzed. Some cells were given a single dose of Lineac irradiation (10 or 20 Gy).
 Production of IL-6 (with or without IL-1β stimulation) increased gradually to a maximum after 72 hours, more in the 20 Gy-irradiated cells than 10 Gy cells (p < 0.01). Production of IL-8 increased gradually to a maximum after 48 or 72 hours. Spontaneous production of IL-8 increased more in 20 Gy-irradiated cells than 10 Gy cells after 6 and 24 hours (p < 0.01), but increased more in 10 Gy cells than 20 Gy cells after 48 and 72 hours (p < 0.01). The production of IL-8 stimulated by IL-1β increased more in 10 Gy cells than 20 Gy cells 24 hours later (p < 0.01). IL-6 and IL-8 production differed in the response to irradiation. Our data suggest that bidirectional communication between the immune system and glioma cells changes after radiotherapy.