To study the effects of grafted induced neural stem cells (iNSCs) on complement activation following traumatic brain injury (TBI).

Healthy adult male C57BL/6 mouse TBI models were established using a standardized weight-drop device. Neurological severity scores (NSS) of 4-8 points was included in TBI group (n=30). Ten TBI mice serum and heat-inactivated TBI mice serum were selected randomly, and the other 20 mice were randomly divided into iNSCs group (n=10) and phosphate buffer saline (PBS) group (n=10). At 12 h after TBI, mice were anaesthetized again and randomly selected to receive 200 μL of cell suspension containing 5×10⁶ cells or PBS intravenously. On day 7 after TBI, animals were sacrificed for morphological analysis. Double-labeling experiments were utilized to determine the effects of iNSC grafts on C3d⁺/NeuN⁺, C5b-9⁺/NeuN⁺, C3d⁺/Map2⁺ and C5b-9⁺/Map2⁺ neurons in the brains of TBI mice. To identify the regulatory effects of iNSCs on complement activation, we utilized flow cytometry to determine Crry, Cd46, Cd59a and Cd55 protein expression levels in iNSCs after TBI or heat-inactivated TBI (HI-TBI) mouse serum treatment.

Double-labelling experiments showed that C3d and C5b-9 immunostaining was detected in the NeuN⁺ and Map2⁺ neurons in the injured cortex. Furthermore, the levels of C3d⁺/NeuN⁺, C5b-9⁺/NeuN⁺, C3d⁺/Map2⁺ and C5b-9⁺/Map2⁺ neurons were significantly lower in the iNSCs group than in the PBS group (P<0.05). Flow cytometry analysis revealed a dramatic increase in Crry expression in iNSCs in the TBI group compared with the HI-TBI group (P<0.05).

Systemic administration of iNSCs could efficiently attenuate the detrimental effects of complement activation on neurons following TBI.