(A) Naïve mice were administered monoclonal anti-PEG IgG (“APA”; n=4) or PBS (“PBS”; n=8) 24 h prior to infusion of PEG-liposomes. Then, 7 days later, blood was collected to quantify APA. (B) Naïve mice (n=4) were treated at Day 0 and blood was collected at Day 7 for the measurement of APA induced by the various treatments. Comparisons across group averages were conducted using unpaired t-tests, with *,**, and *** representing p<0.05, 0.01, and 0.001, respectively. NS; no significant difference.