C4B and myeloid sarcoma: However, as we have previously mentioned, CD46 is also a member of the complement regulatory protein family that confers protection against activated complement-mediated lysis by inactivating C3b/C4b deposited on the membrane of autologous cells; therefore, the increased levels of CD46 demonstrated in the serum and CSF of patients with MS may be indicative of an increased activation of the complement system in MS, both peripherally and intrathecally, and lend further support to the possible contribution of complement in disease pathogenesis.