Differential detection of PAS-positive inclusions formed by ... : Hepatology (original) (raw)

Original Articles

Differential detection of PAS-positive inclusions formed by the Z, Siiyama, and Mmalton variants of α1-antitrypsin

Janciauskiene, Sabina*,1,†; Eriksson, Sten1; Callea, Francesco2; Mallya, Meera3; Zhou, Aiwu3; Seyama, Kuniaki4; Hata, Satoru5; Lomas, David A.3

1Department of Medicine, University Hospital Malmö, Malmö, Sweden

2Department of Pathology, Children’s Hospital Bambino Gesu, Rome, Italy

3Departments of Medicine and Haematology, University of Cambridge, Cambridge Institute for Medical Research, Cambridge, United Kingdom

4Department of Respiratory Medicine, Juntendo University School of Medicine, Tokyo, Japan

5Clinical Laboratory, Nagano Red Cross Hospital, Nagano, Japan

E-mail:[email protected]

*Address reprint requests to: Department of Medicine, University of Lund, SE-205 02 Malmö, Sweden.

†fax: (46) 40-337041

Received May 04, 2004; Accepted July 06, 2004; previously published online October 14, 2004

Abstract

Several point mutations of α1-antitrypsin cause a perturbation in protein structure with consequent polymerization and intracellular accumulation. The retention of polymers of α1-antitrypsin within hepatocytes results in protein overload that in turn is associated with juvenile hepatitis, cirrhosis, and hepatocellular carcinoma. The detection of α1-antitrypsin polymers and understanding the molecular basis of polymer formation is of considerable clinical importance. We have used a monoclonal antibody (ATZ11) that specifically recognizes a conformation-dependent neoepitope on polymerized α1-antitrypsin to detect polymers within hepatocytes of individuals with α1-antitrypsin deficiency. Paraffin-embedded liver tissue specimens were obtained from individuals who were homozygous for the Z (Glu342Lys), Mmalton (52Phe del), and Siiyama (Ser53Phe) alleles of α1-antitrypsin that result in hepatic inclusions and profound plasma deficiency. Immunohistological staining with a polyclonal anti-human α1-antitrypsin antibody showed hepatic inclusions in all 3 cases, while ATZ11 reacted with hepatic inclusions formed by only Z α1-antitrypsin. Polymers of plasma M and Z α1-antitrypsin prepared under different conditions in vitro and polymers of recombinant mutants of α1-antitrypsin demonstrated that the monoclonal antibody detected a neoepitope on the polymerized protein. It did not detect polymers formed by a recombinant shutter domain mutant (that mirrors the effects of the Siiyama and Mmalton variants), polymers formed by cleaving α1-antitrypsin at the reactive loop, or C-sheet polymers formed by heating α1-antitrypsin in citrate. In conclusion, the ATZ11 monoclonal antibody detects Z α1-antitrypsin in hepatic inclusions by detecting a neoepitope that is specific to the polymeric conformer and that is localized close to residue 342. (Hepatology 2004;40:1203-1210.)