Introduction IgG4 mediated autoimmune disease has recently been described in relation to pancreatitis and sclerosing cholangitis. Furthermore recent reports, mainly from Japan, have also identified cases of autoimmune hepatitis (AIH) in which an IgG4 positive hepatic inflammatory infiltrate predominates.

Methods We set out to establish the frequency with which IgG4 +ve plasma cells are observed in a cohort of patients with AIH without pancreatitis or sclerosing cholangitis. Immuno-histochemical analysis via application of a monoclonal antibody to IgG4 was undertaken on archived liver tissue specimens. Three fields per biopsy specimen were analysed and the number of IgG4 +ve plasma cells per high powered field (HPF) and the proportion of these as a total of the plasma cell infiltrate were recorded. As per recent publications^{1 2} a biopsy specimen was determined to be IgG4 +ve if more than 10 IgG4 +ve plasma cells were seen per high powered filed (HPF) AND where this number equated to >40% of the total plasma cell infiltrate. Immunohistochemical and histo-pathological analysis was undertaken by a single, experienced, hepato-pathologist (YZ).

Results Sixty-three liver tissue specimens underwent immuno-histochemical analysis. These specimens derived from 53 Caucasian and 10 Afro-Caribbean patients. All patients met the revised International Autoimmune Hepatitis Group diagnostic criteria for probable or definite AIH. The median age of patients at diagnosis was 31 years and 78% were female. Among this cohort 44 patients presented with chronic disease and histological evidence of chronic active hepatitis while 19 presented with acute disease in whom histology demonstrated hepatic collapse in 16 and severe lobular hepatitis in three patients. Only 7 of 63 samples (11%) demonstrated >10 IgG4 +ve cells/HPF. While there was a greater number of biopsy specimens with >10 IgG4 +ve plasma cells per HPF in acute vs chronic presentations this did not reach statistical significance (16% vs 9%, p=0.44). Additionally, there was no difference in the frequency of this finding between males and females (males 21% females 8% p=0.4) or between different ethnic groups (11% in Caucasians vs 10% in Afro-Caribbeans, p=0.99). Importantly, in none of the seven cases in which >10 IgG4 +ve plasma cells/HPF were noted did the proportion of IgG4 +ve plasma cells equate to >40% of the total plasma cell infiltrate.

Conclusion While a small proportion of non-Asian AIH patients demonstrate >10 IgG4 +ve plasma cells/HPF, in no individual did this represent >40% of the total hepatic plasma cell infiltrate. Consequently, significant IgG4 +ve plasma cell infiltrates are not observed among non-Asian patients with AIH presenting to our institution.

Competing interests None declared.

References 1. Umemura T, et al. Hepatology 2007;46:463–71.

2. Cheuk, et al. Adv Anat Pathol 2010;17:303–32.