Protective effects of anti-C5a in sepsis-induced thymocyte apoptosis

Multiorgan apoptosis occurs during sepsis. Following cecal ligation and pun cture (CLP) in rats, thymocytes underwent apoptosis in a time-dependent man ner. C5a blockade dramatically reduced thymocyte apoptosis as measured by t hymic weight, binding of annexin V to thymocytes, and laddering of thymocyt e DNA. When C5a mas generated in vivo by infusion of purified cobra venom f actor (CVF), thymocyte apoptosis was significantly increased. Similar resul ts were found when CVF was injected in vivo during the early stages of CLP. In animals 12 hours after induction of CLP, there was an increase in the a ctivities of caspase-3, -6, and -9, but not caspase-1 and -8. Cytosolic cyt ochrome c levels increased by twofold, whereas mitochondrial levels showed a 50% decrease. Western blot analysis revealed that the content of Bcl-X-L (but not of Bcl-2, BAX, Bad, and Bim) significantly decreased in thymocytes after CLP. C5a blockade in the sepsis model almost completely inhibited ca spase-3, -6, and -9 activation, significantly preserved cytochrome c in the mitochondrial fraction, and restored Bcl-XL expression. These data suggest that systemic activation of complement induces C5a-dependent apoptosis of thymocytes and that the blockade of C5a during sepsis rescues thymocytes fr om apoptosis.