Diagnostic Relevance and Clinical Significance of the New Enhanced Performance M2 (MIT3) ELISA for the Detection of IgA and IgG Antimitochondrial Antibodies in Primary Biliary Cirrhosis

Abstract

The new IgG and IgA MIT3-based ELISAs seem to have higher specificity and sensitivity for AMA detection than IIF and the conventional anti-M2. Interestingly, these assays were able to unmask AMA presence in almost half of the AMA-negative samples by IIF. These findings may suggest the use of MIT3-based ELISAs as first-line investigation for AMA detection, particularly, when the laboratories are unfamiliar with the use and interpretation of the IIF patterns of AMA. The presence of IgG AMA seems to characterize PBC patients with more severe disease, but both IgG and IgA isotypes of AMAs were not predictive markers of disease outcome.

Primary biliary cirrhosis in HBV and HCV patients: Clinical characteristics and outcome

“…These data suggest that existence mostly of biochemical indices of cholestasis should prompt physicians to sick for AMA with various sensitive techniques as well as for PBC-specific ANA irrespective of the presence or not of other liver diseases [12,20,22,25,29] . Since the discovery of AMA, their subsequent inclusion in "routine" autoantibody testing, has led to PBC being more frequently diagnosed at an earlier stage of disease progression being mainly asymptomatic [7,12,19,20,25] .…”

“…In all but two patients with chronic HBV and HCV infections described in our study PBC was diagnosed during the follow-up period for viral hepatitis. The diagnosis of PBC was based in all patients on the presence of elevated cholestatic enzymes and AMA identified either by IIF and immunoblot or by a sensitive MIT3-based ELISA (IgG and IgA) and immunoblot, in those being AMA negative by IIF [12,19,20,22] . In addition, ANA specific for PBC, identified in two of these patients, could serve not only as diagnostic tools for PBC but also as prognostic markers of the disease [12,25,29] .…”

“…Since the discovery of AMA, their subsequent inclusion in "routine" autoantibody testing, has led to PBC being more frequently diagnosed at an earlier stage of disease progression being mainly asymptomatic [7,12,19,20,25] . Indeed, up to 60% of PBC patients are reported to be asymptomatic at diagnosis with less severe disease in terms of liver biochemistry and histology compared to symptomatic patients [7,12,19,20,22,26,30] . In accordance with this, the repetitive presence of AMA in our patients, who were mostly asymptomatic, may well signify that PBC was in its early stages.…”

“…According to internationally accepted criteria and to previous publications from our group [12,[19][20][21] , patients with PBC met at least two of the following criteria: (1) positivity for antimitochondrial antibody (AMA; positive titre ≥ 1/40) either by IIF on in-house rodent tissue substrates confirmed by Western blot using in-house mitochondrial subfraction of rat livers, or by enhanced performance M2 ELISA (M2 EP (MIT3) ELISA, Quanta Lite, INOVA Diagnostics, San Diego, CA), which was shown to have higher sensitivity compared to the conventional anti-M2 [20,22] ; (2) elevated cholestatic enzymes and (3) histological lesions of PBC (when a liver biopsy had been performed). The presence of other liver diseases and in particular of AIH has been appropriately excluded [8,23] .…”

“…A liver biopsy was performed in 12 of 17 patients and had PBC features in 3 of them. In terms of AMA positivity, 14 patients were AMA positive by IIF confirmed by immunoblot, while 3 patients being persistently AMA negative by IIF were found to be repeatedly anti-M2 positive tested by the enhanced performance MIT3-based ELISA and immunoblot [20,22] . Two out of 17 patients had also ANA with reactivity against multiple nuclear dots (MND), which is considered specific for PBC [12,25] .…”