Transient infiltration of neutrophils into the thymus in association with apoptosis induced by whole-body X-irradiation

Generally, the process of apoptosis does not cause leakage of noxious cytos olic contents and is therefore non-inflammatory, However, as previously sho wn, macrophages ingesting apoptotic CTLL-2 cells produced pro-inflammatory cytokines, particularly interleukin-8 (IL-8) and macrophage inflammatory pr otein-2 (MIP-2), a murine IL-8 homolog, This predicted that rapid and massi ve apoptosis may induce neutrophil accumulation in vivo. In this study, we tested this prediction by inducing apoptosis by whole-body X-irradiation in mice. After exposure to 4 Gy X-ray irradiation, mice exhibited considerabl e apoptosis of thymic cells, which was associated with transient infiltrati on of neutrophils as well as MIP-2 mRNA expression, In contrast, in p53-def icient mice in which irradiation-induced apoptosis was suppressed, as has b een reported, infiltration of neutrophils into the thymus was less than tha t found in P53(+/+) mice. Taken together, these results suggest that massiv e and rapid apoptosis can result in infiltration of neutrophils.