The liver is populated by a broad spectrum of markers for macrophages. In alcoholic hepatitis the macrophages are M1 and M2

Abstract

Background: Liver cell injury in alcoholic hepatitis (AH) is in part, due to macrophage generated proinflammatory cytokines i.e., M1, M2a, M2b, and M2c might be involved in ALD. The T cell response to chemokines and cytokines differs not only when M1 and M2 macrophages are compared but even when individual M2 subtypes are profiled.

Purpose: In AH, M1 monocytes in the blood show increased sensitivity in the TNF-α response to LPS. Immunohistochemistry (IHC) studies showed that the liver sinusoids in ALD are abundantly populated by CD163 expressing type 2 macrophages. In this report, we profile many of the molecules associated with M1 and M2 macrophages in livers with AH using IHC.

Methods: Using immunofluorescent antibody-labeling, we profiled the receptors, cytokines and chemokines observed in M1, M2a, M2b, and M2c macrophages in liver biopsies from patients with AH.

Results: The increased CD 163 expression found in previous studies was confirmed as well an additional macrophage phenotypic marker CD206, suggesting that AH pathogenesis at least partially involves M2a and M2c macrophages. TGF-β was found to be robustly over expressed by liver sinusoidal macrophages. Macrophage expression of the phenotypic markers TLR-2, TLR-4 and TLR-8 - found in both M1 and M2 macrophages - as well as the chemokines CCL-1 and CCL-18 was found. However, IRF-4, which is related to IL-4 production and M2a polarization as well as the cytokines CCL-1 and Il-1β and the chemokine CXCL-1 were also observed, suggesting that M2a and M2b also play a role in AH pathogenesis.

Conclusion: Livers with AH show robust macrophage over expression of TGF-β, a growth factor more commonly associated with M2 type macrophages and mostly known for its fibrogenetic properties. However, our immunoprofiling of macrophage over expression also shows that AH is driven by receptors, interferons, and cytokines that are commonly associated not just with M2 macrophages, but with M1 as well. Thus, a complex interplay between different types of macrophages expressing a diverse array of molecules and receptors is involved in AH.

Keywords: Alcoholic hepatitis; CD163; Macrophages; TLR-4.