Objectives. Taking into account that genetic predisposition, marked by human leukocyte antigen (HLA) class I and II genes, augments the probability of developing an autoimmune disorder after a triggering vaccination, as largely debated, we investigated the frequency of autoantibody production after recombinant hepatitis B vaccine (rHBv) in 6-year-old children immunized at birth to evaluate an association between autoimmune disorders and hepatitis B virus vaccination.

Methods. We investigated the presence of autoantibodies in 210 6-year-old children who were immunized at birth with rHBv: 200 showed anti-hepatitis B surface antigen concentrations ≥10 mUI/mL at seroconversion (responders), and 10 were nonresponders. Data were compared with those obtained in 109 unvaccinated children. All participants were screened for the presence of antinuclear antibodies (ANAs), anti-DNA, antimitochondrial, anti-liver/kidney microsomal, antireticulin, anti-smooth muscle (SMA), and antiribosomal antibodies. All participants were also screened for the presence of antithyroid antibodies, such as antithyroglobulin and antiperoxidase, and for antibodies found in type 1 diabetes, such as tyrosine phosphatase (IA-2A) and glutamic acid decarboxylase (GADA). HLA typing was extended to all 10 nonresponders.

Results. Autoantibodies were found in 16 of the 200 responders: ANAs were found in 12 (6%), smooth muscle antibodies were found in 4 (2.0%), and antireticulin antibodies and endomysial antibodies were found in 1 girl with ANAs. Antithyroid antibodies, IA-2A, and GADA were not present in any of the participants. No significant difference was found in the frequency of autoantibodies between vaccinated and control children. Three of the 10 nonresponder children were SMA-positive (30% vs 2% of responders); they also carried the supratype HLA-C4AQ0,DRB1*0301,DQB1*02. A family history for autoimmune disorders was present in 3 (18%; 95% confidence interval [CI]: 4.0%–45.6%) of the 16 responder infants with autoantibodies, in 15 (8.4%; 95% CI: 4.6%–13.1%) of responder children without autoantibodies, and in 1 (10%) of the 10 nonsreponder children.

Conclusions. From our data, vaccination with rHBv given during the neonatal period does not seem to increase autoantibody production in a 6-year-old children. Autoantibodies, referred to as natural autoantibodies, can be found in healthy participants, but their significance is unclear. These autoantibodies often cross-react with bacteria or tumor antigens, suggesting their importance in innate immunity. It has been demonstrated in an animal model that self-antigen can promote B-cell accumulation, and that a significant proportion of natural autoantibodies is the product of this self-antigen- dependent process. Consequently, it has been speculated that self-antigens play a positive role in recruiting B cells as a part of innate immunity, but this process carries a potential risk for unregulated growth.

Spreading of the immune response is a common theme in organ-specific and systemis autoimmune diseases, and this could be initiated by exogenous agents, in genetically susceptible hosts, owing to molecular mimicry of natural antigen. Moreover, 3 (18%) of the 16 children who had autoantibodies had a family history of autoimmume diseases. Thus, it is apparent that susceptibility to autoimmunity is determined by genetic factors rather than by vaccine challenge. Among all the children considered, only 1 girl (0.5%) developed celiac disease, reflecting the prevalence described in the literature. GADA and IA-2A were not found in our children; this observation is in agreement with data showing that type 1 diabetes risk may not be altered by vaccinations administered during childhood. On the contrary, a high frequency (30%) of autoantibodies, in particular SMA, was observed in the nonresponder children. The 3 SMA-positive children carried the HLA-C4Q0,DRB1*0301,DQB1*02 haplotype, a well-known predisposing factor for autoimmune disorders. On the other hand, the presence of autoantibodies to smooth muscle is known to be common in hepatitis B infection, and, it has been shown that cross-reactive immunity targeting homologous self-protein may partly account for autoantibody production. Although hepatitis B vaccination given during the neonatal period does not increase autoantibody production in 6-year-old immunized children, we deem useful a more prolonged follow-up for these nonresponder children carrying certain HLA haplotypes (such as C4AQ0,DRB1*0301,DQB1*02), particularly because most autoimmune diseases do not develop until later in life.

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