Human 291J6 IgG was expressed in silkworm using a Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid system. The mean amounts of 2961,16 IgG produced in larval hemolymph and whole pupae were 30.1 mu g/larva and 78.0 mu g/pupa, respectively. The use of molecular chaperones including calreticulin (CRT), calnexin (CNX), and immunoglobulin heavy chain binding protein (BiP, GRP78) improved the production of 2961J6 IgG secretion in the larvae fivefold. The total yield of recombinant 291J6 IgG was 239 mu g/mL when coexpressed with CRT. However, the overexpression of molecular chaperones had negative effects on secretion. The N-linked glycans of secreted 2961J6 IgG in silkworm hemolymph were dominated by paucimannose structures. Small amounts of GlcNAc residues linked to the Man alpha 1,3 branch were detected. When molecular chaperones were coexpressed, the compositions of N-linked glycans in the IgG1 produced were unchanged compared with those produced without them. This suggests that N-glycosylation is controlled by a regulatory function in the Golgi apparatus even though the post-translational modification of 2961J6 IgG was assisted by the coexpression of molecular chaperones. Therefore, if the glycosylation pathways that coexpress N-acetylglucosaminyltransferase, galactosyltransferase, and sialyltransferase could he improved, silkworm larvae might prove a useful system for producing human antibodies. (C) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 26: 232-238, 2010