When lepidopteran larvae are infected by a large quantity of pathogens or parasitized by nonadaptive parasitoids hemocytes in the hemocoel will encapsulate these foreign invaders Cellular encapsulation requires hemocytes particularly plasmatocytes to change their states from nonadhesive spherical cells into adhesive spreading cells However It is unclear how the changes of plasmatocytes are regulated Here we report that the integrin beta 1 subunit from hemocytes of Ostrinia furnacalis (Ofint beta 1) plays an important role in regulating the spreading of plasmatocytes The full length cDNA sequence (4477 bp) of Ofint beta 1 was cloned from hemocytes Phylogenetic analysis showed that Ofint beta 1 belonged to the integrin beta PS family of Drosophila melanogaster with highest sequence identity (78 7%) to the beta-integrin of Pseudoplusia includens Structural analysis of the deduced amino acid sequence indicated that Ofint beta 1 had similar functional domains to known beta-integrins in other lepidopteran insects RT-PCR Northern blotting Western blotting and immunohistochemical analyses showed that OfINT beta 1 was expressed mainly in hemocytes especially in plasmatocytes and weakly in fat body Malpighian tubes and epidermis After hemocytes had spread onto slides fewer antibodies to OfINT beta 1 bound to the surface of plasmatocytes Furthermore anti-OfINT beta 1 serum clearly inhibited the spreading of plasmatocytes Together these results indicate that OfINT beta 1 may play an important role in regulating the spreading of plasmatocytes (C) 2010 Elsevier Ltd All rights reserved