Multiple α 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 (Ig) superfamily (neuroglian) are involved in the encapsulation response of hemocytes in Manduca sexta. In addition, two new integrin alpha (α) subunits have been found on these hemocytes. The α2 subunit is mainly expressed in epidermis and Malphigian tubules, whereas the α3 subunit is primarily expressed on hemocytes and fat body cells. Of the three known α subunits, the α1 subunit found in HS integrin is the predominant subunit of hemocytes. Cell adhesion assays indicate that α2 belongs to the integrin family with RGD-binding motifs, confirming the phylogenetic analysis of α subunits based on the amino-acid sequence alignment of different α subunits. Double-stranded RNAs (dsRNAs) targeting each of these three integrin α subunits not only specifically decreased transcript expression of each α subunit in hemocytes, but also abolished the cell-mediated encapsulation response of hemocytes to foreign surfaces. The individual α subunits of M. sexta integrins, like their integrin counterparts in mammalian immune systems, have critical, individual roles in cell-substrate and cell-cell interactions during immune responses.