Opposite effects of donor apoptotic versus necrotic splenocytes on splenic allograft tolerance

Apoptotic cells have immunosuppressive activity, whereas necrotic cells activate immune response, indicating they might have different effects on immune rejection against splenic allografts. The aim of this study was to determine whether administration of apoptotic or necrotic splenocytes of donor origin could impact the acute rejection of splenic allografts.

Apoptotic or necrotic splenocytes derived from donor rats were induced by irradiation or freeze thaw, respectively. Heterotopic vascularized spleen transplantation was performed from Wistar-Furth (donor) to Sprague-Dawley (recipient) rats, and splenocytes were intravenously injected into the recipients. At different time points, the recipients were sacrificed and the splenic allografts underwent histological examination. The interferon-gamma (IFN-gamma) and transforming growth factor-beta1 (TGF-beta1) in sera, spleens of recipients, and donor splenocytes before administration were measured. Mixed leukocyte reaction (MLR) was detected with recipient splenocytes as effectors and donor splenocytes as stimulators.

Exposure to gamma-irradiation at dose of 10,000 rad caused over 80% splenocytes to become apoptotic. The levels of TGF-beta1 released by apoptotic splenocytes in vitro were significantly higher than that by untreated splenocytes, whereas there was almost no TGF-beta1 detected in necrotic splenocytes culture medium. Administration of apoptotic splenocytes significantly attenuated acute rejection of splenic allografts, evidenced by less severe splenic histological alteration and reduction of histological scores compared with control; whereas necrotic splenocytes exacerbated the acute rejection. Apoptotic splenocytes inhibited production of IFN-gamma but increased the levels of TGF-beta1, whereas necrotic splenocytes showed opposite activity in production of those cytokines. Administration of apoptotic splenocytes inhibited MLR, and necrotic splenocytes promoted MLR.

The apoptotic and necrotic splenocytes exhibited opposite effects on acute rejection against splenic allografts, and IFN-gamma and TGF-beta1 have been involved in the effects.