Table 1 Biosynthesis of secreted innate immunity proteins by hepatocytes.

From: Hepatocytes: a key cell type for innate immunity

Innate Immunity proteins

Mainly synthesized in hepatocytes

Function

References

 

Classical

C1r/s, C2, C4, C4bp

Activate C classical pathway

13,14

 

Alternative

C3, B

Activate C alternative pathway

13,14,15

Cs

Lectin

MBL, MASP1, 2 3, MAp19

Activate C MBL pathway

16,17,18

 

Terminal

C5, C6, C8, C9

Terminal C components

13,14

 

Regulators

I, H, C1-INH

Inhibit C activation

13

Opsonins

Pentraxins

CRP, SAP

Bind to microbes and subsequently activate Cs and phagocytosis to kill microbes

19,20,21,35

 

SAA

SAA

Binds to the outer membrane protein A family members on bacteria to activate phagocytosis

24,25

LPS signaling regulators

Lipid transferase

LBP

Binds to LPS and subsequently transfers LPS to a receptor complex (TLR4/MD-2) via a CD14-enhanced mechanism

51,52,53

 

sCD14

Soluble CD14

Stimulates or inhibits LPS signaling depending on its concentration and environment

54,55,56,57

 

sMD-2

Soluble MD-2

Stimulates or inhibits LPS signaling depending on its concentration and environment

58,59

Iron metabolism

Iron-carrying protein

Transferrin

Binds to free iron, limiting iron availability to pathogens

86

-related proteins

Lipocalin-2

Lipocalin-2

Attenuates iron uptake by bacteria via binding to siderophores

94,95,96,97

 

Anti-microbial peptide

Hepcidin (also LEAP)

Anti-microbial peptide via limiting iron availability

108,109

 

Hemopexin

Hemopexin

Retains heme from the bacteria by binding to heme

103

Others

Clotting factors

Fibrinogen

A central regulator of the inflammatory response

111

 

PGRPs

PGLYP2

Anti-inflammatory response via digestion of peptidoglycan on the bacterial wall

160,161

 

Proteinase inhibitors

AAT, ACT, α1-CPI, α2M

Inactivate proteases released by pathogens and dead or dying cells

124,125,126

  1. α1-CPI, α1-cysteine proteinase inhibitor (thiostain); α2M, α2-macroglobulin; AAT, antitrypsin; ACT, antichymotrypsin; B, factor B; C1-INH, C1 inhibitor; CRP, C-reactive protein; Cs, complements;, I, factor I; H, factor H; LBP, LPS-binding protein; LEAP, liver expressed antimicrobial peptide; MBL, mannan-binding lectin; MASP, mannan-binding lectin-associated serine proteases; PGRPs, peptidoglycan-recognition proteins; PGLYP2, peptidoglycan-recognition protein-2; SAA, serum amyloid A; SAP, serum amyloid P.
Back to article page