Faculty Bibliography

Complements, such as C1q and C3, and macrophages in the splenic marginal zone (MZMs) play pivotal roles in the efficient uptake and processing of circulating apoptotic cells. SIGN-R1, a C-type lectin that is highly expressed in a subpopulation of MZMs, regulates the complement fixation pathway by interacting with C1q, to fight blood-borne Streptococcus pneumoniae. Therefore, we examined whether the SIGN-R1-mediated classical complement pathway plays a role in apoptotic cell clearance and immune tolerance. SIGN-R1 first-bound apoptotic cells and this binding was significantly enhanced in the presence of C1q. SIGN-R1-C1q complex then immediately mediated C3 deposition on circulating apoptotic cells in the MZ, leading to the efficient clearance of them. SIGN-R1-mediated C3 deposition was completely abolished in the spleen of SIGN-R1 knockout (KO) mice. Given that SIGN-R1 is not expressed in the liver, we were struck by the finding that C3-deposited apoptotic cells were still found in the liver of wild-type mice, and dramatically reduced in the SIGN-R1 KO liver. In particular, SIGN-R1 deficiency caused delayed clearance of apoptotic cells and aberrant secretion of cytokines, such as TNF-α, IL-6, and TGF-β in the spleen as well as in the liver. In addition, anti-double- and single-stranded DNA antibody level was significantly increased in SIGN-R1-depleted mice compared with control mice. These findings suggest a novel mechanism of apoptotic cell clearance which is initiated by SIGN-R1 in the MZ and identify an integrated role of SIGN-R1 in the systemic clearance of apoptotic cells, linking the recognition of apoptotic cells, the opsonization of complements, and the induction of immune tolerance.

Relaxin (RLX) has multiple vascular actions, including vasodilation and angiogenesis, which occur via induction of vascular endothelial growth factor (VEGF) expression. We generated a RLX-expressing (dE1-RGD/lacZ/RLX) adenovirus and investigated whether it enhances skin flap survival. Thirty Sprague-Dawley rats were divided into three groups: RLX-expressing adenovirus group, control virus group, and phosphate-buffered saline (PBS) group. Two days before surgery and immediately after flap elevation, the caudally based flap that was 3 × 9 cm in size was subdermally injected with the dE1-RGD/lacZ/RLX virus (10⁷ PFU), dE1-RGD/lacZ virus (10⁷ PFU), or PBS. The surviving area of the flap and the amount of blood flow were measured. On postoperative day 10, CD31-positive vessels and VEGF protein expression were examined. We observed a significant increase in the survival area of the flap in the RLX group. Doppler measurement also showed significantly increased blood flow immediately after the operation and on postoperative days 7 and 10. CD31-positive vessels and VEGF protein expression were significantly greater in the RLX group. Thus, administration of RLX-expressing adenovirus into elevated skin flaps increased VEGF expression, the number of capillaries, and blood flow to the flap, thereby improving skin flap survival.