To assess in vivo chemotactic activity of tumour necrosis factor (TNF), interleukin‐1 (IL‐1), IL‐8, and cytokine‐induced neutrophil chemoattractant (CINC), we injected these cytokines into the pleural cavity of rats.
CINC (0.1‐1 μg) and recombinant human IL‐8 (rhIL‐8, 0.2–5 μg) caused neutrophil infiltration into the rat pleural cavity in a dose‐dependent fashion, peaking at 3 h. The number of leukocytes in the peripheral blood did not change significantly.
RhTNFα and rhIL‐1α also induced neutrophil accumulation. The dose response curves of rhTNFα (0.67 ng‐6.7 μg) and rhIL‐1α (0.45 ng‐4.5μg) at 3 h were bell shaped. On the other hand, unlike CINC and rhIL‐8, rhTNFα and rhIL‐1α caused transient marked leukopenia at 3 h in a simple dose‐dependent fashion.
Concomitant injection of actinomycin D dose‐dependently and completely at 10 μg inhibited neutrophil infiltration induced by rhTNFα (0.67 μg) and rhIL‐1α (0.45 μg) at 3 h. However, that induced by CINC or rhIL‐8 was not affected by actinomycin D.
Peaking at 1 h, CINC production in the pleural cavity was found after intrapleural injection of rhTNFα (0.67 μg) or rhIL‐1α (0.45 μg), but not after that of rhIL‐8 (5 μg). The CINC production induced by rhTNFα or rhIL‐1α and the neutrophil infiltration was suppressed by concomitant injection of actinomycin D (1 and 10 μg).
These results indicate that CINC and IL‐8 themselves are direct chemoattractants for neutrophils, whereas TNF and IL‐1 induce neutrophil infiltration indirectly via newly synthesized mRNA for chemotactic protein including CINC, which may be involved in neutrophil emigration at local inflammatory sites in rats.