CD Markers and Complement

• CD2


  Involved in T cell activation
• CD3


  Associated with T cell antigen receptor; role in TCR transduction
• CD4


  Co-receptor for MHC class II; receptor for HIV
• CD5


  Positive or negative modulation of T and B cell receptor signaling
• CD8


  Co- receptor for MHC class I
• CD10


  Protease; marker for pre-B CALLA
• CD16


  Low affinity Fc receptor, mediates phagocytosis and ADCC
• CD19


  Part of B cell co-receptor; signal transduction molecule that regulates B cell development and activation
• CD21


  Receptor for complement component C3d; part of B cell co-receptor with CD 19
• CD23


  Regulation of IgE synthesis; triggers release of GM-CSF from monocytes
• CD25


  Receptor for IL-2
• CD44


  Adhesion molecule mediating homing to peripheral lymphoid organs
• CD45R


  Essential in T and B cell antigen-stimulated activation
• CD56


  Not known
• CD94


  Subunit of NKG2-A complex involved in inhibition of NK cell cytotoxicity
• C1q


  Binds to Fc of IgM and IgG – recognizes the Fc portion of antibody
• C1r


  Activates C1s
• C1s


  Cleaves C4 and C2
• C4


  Part of C3 convertase (C4b) Second most abundant complement component
• C2


  Binds to C4b – form C3 convertase
• C3


  KEY INTERMEDIATE AND PIVOTAL POINT IN ALL PATHWAYS Most abundant complement component
• C5


  Initiates membrane attack complex
• C6


  Binds to C5b in MAC
• C7


  Binds to C5bC6 in MAC
• C8


  Starts pore formation on membrane
• C9


  Polymerizes to cause cell lysis
• Factor B


  Binds C3b to form C3 convertase
• Factor D


  Cleaves factor B
• Properdin


  Stabilizes C3 convertase and C5 convertase in the presence of Mg2+
• MBL


  Binds to mannose
• MASP-1


  Helps cleave C4 and C2
• MASP-2


  Cleaves C4 and C2
• C1 Inhibitor (C1INH)


  Dissociates C1r and C1s from C1q
• Factor I


  Cleaves C3b and C4b
• Factor H


  Cofactor with I to inactivate C3b, prevents binding of B to C3b The principal soluble regulator of the alternative pathway
• C4- binding protein


  Acts as a cofactor with I to inactivate C4b
• S protein (Vitronectin)


  Prevents attachment of the C5B67 complex to cell membrane
• DAF(CD55)


  Dissociates C2b or Bb from binding sites, thus preventing formation of C3 convertase
• MIRL(CD59)


  Prevents insertion of C9 into cell membran
• CR1 (CD35)

  Cofactor with I; mediates transport of immune complexes It is found mainly on peripheral blood cells It binds C3b and C4b but has the greatest affinity for C3b.Once bound to CR1, both C4b and C3b can then be degraded by Factor I.