2.1. Materials
Eight-arm PEG N-hydroxysuccinimide ester with an Mw of 10 kDa (8-arm
PEG), 6-maleimidohexanoic acid N -hydroxysuccinimide ester (EMCS),
iminothiolane hydrochloride (IT), and 3,3’,5,5’-tetramethylbenzidine
(TMB) were purchased from Sigma-Aldrich (USA). CRM197was kindly provided by Hualan Biological Engineering, Inc. (China). The
RPMI 1640 medium and fetal bovine serum (FBS) were purchased from Gibco
(USA). Horseradish peroxidase-conjugated goat anti-mouse IgG Fc antibody
(HRP-IgG), IgG1 Fc antibody (HRP-IgG1), IgG2a Fc antibody (HRP-IgG2a)
and IgM Fc antibody (HRP-IgM) were ordered from Abcam (USA). IFN-γ and
IFN-β ELISA kits were ordered from Legend (USA). TNF-α and IL-5 ELISA
kits were ordered from Invitrogen (USA). All other reagents were of
analytical grade.