Multiple alpha subunits of integrin are involved in cell-mediated responses of the Manduca immune system

The cell-mediated responses of the insect innate immune system-phagocytosis, nodulation, encapsulation-involve multiple cell adhesion molecules of hemocyte surfaces. A hemocyte-specific (HS) integrin and a member of the immunoglobulin (1g) superfamily (neuroglian) are involved in the encapsulation response of hemocytes in Manduca sexta. In addition, two new integrin alpha (alpha) subunits have been found on these hemocytes. The alpha 2 subunit is mainly expressed in epidermis and Malphigian tubules, whereas the alpha 3 subunit is primarily expressed on hemocytes and fat body cells. Of the three known a subunits, the alpha 1 subunit found in HS integrin is the predominant subunit of hemocytes. Cell adhesion assays indicate that alpha 2 belongs to the integrin family with RGD-binding motifs, confirming the phylogenetic analysis of a subunits based on the amino-acid sequence alignment of different a subunits. Double-stranded RNAs (dsRNAs) targeting each of these three integrin a subunits not only specifically decreased transcript expression of each a subunit in hemocytes, but also abolished the cell-mediated encapsulation response of hemocytes to foreign surfaces. The individual a subunits of M. sexta integrins, like their integrin counterparts in mammalian immune systems, have critical, individual rotes in celt-substrate and cell-cell interactions during immune responses. (c) 2007 Elsevier Ltd. All rights reserved.