The impact of PEGylation on protein immunogenicity

► Efficacy of PEG in reducing the immunogenicity of foreign proteins was evaluated. ► PEGylated antibodies immunogenicity was monitored in two strains of mice. ► The influence of PEGylation was found to be inconsistent. ► In contrary to the general assumption, PEG may increase protein immunogenicity. ► PEGylation impact on immunogenicity must be tested on an individual case basis.