# Case report: anti-fibrillarin autoantibodies induced by viral molecular mimicry in a paediatric patient

## TL;DR

A 14-year-old girl developed anti-fibrillarin antibodies linked to an Epstein-Barr virus infection, showing how viral proteins can mimic human proteins and cause temporary autoimmunity.

## Contribution

This case demonstrates how viral molecular mimicry can induce transient anti-fibrillarin autoantibodies in pediatric patients.

## Key findings

- Anti-fibrillarin antibodies were detected alongside EBV infection in a pediatric patient.
- Autoimmunity tests became negative after EBV infection resolved, indicating transient autoimmunity.
- Molecular mimicry between fibrillarin and EBV proteins is suggested as a mechanism.

## Abstract

Anti-fibrillarin autoantibodies (AFA) as serological hallmarks of systemic sclerosis, mainly react with epitopes arranged in the NH2-(aa-1–80) and COOH-terminal-(aa-276–321)-domains of fibrillarin. Interestingly, the fibrillarin NH2-hexapeptide sequence is shared with an Epstein-Barr-virus (EBV)-encoded nuclear antigen.

We herein report a case of a 14-year-old girl presenting with a history of vomiting, sore throat, arthralgias and fever. Laboratory tests revealed leukocytosis, an increased level of CRP, transaminases and total/direct bilirubin. On further investigation, a positivity of ANA testing showing a clumpy nucleolar indirect immunofluorescence (AC-9) pattern on HEp-2000 substrate, due to anti-fibrillarin antibodies, was found. Concomitantly, high concentrations of EBV-VCA-IgM and a slight increase of EBV-VCA-IgG were detected, helping establish a diagnosis of ongoing EBV infection. After a follow-up of six months, all autoimmunity tests were repeated, and together with infection resolution, the negativity of ANA was determined, confirming the transient nature of the autoimmune phenomenon.

Our findings confirm how molecular mimicry plays an important role in the viral-induced autoimmunity. Given the significant homology between fibrillarin and EBV protein sequences, caution in interpreting AFA positivity is suggested, especially in pediatric patients without clinical evidences of an autoimmune condition, and a simultaneous screening for EBV infections is recommended.