Monoclonal antibody MS13 identifies a plasmatocyte membrane protein and inhibits encapsulation and spreading reactions of Manduca sexta hemocytes

Lepidopterans generally can successfully defend themselves against a variet y of parasites or parasitoids, One mechanism they use is to encapsulate the invader in many layers of hemocytes, For encapsulation to occur, the hemoc ytes must attach to the foreign material, spread, and adhere to each other. The molecules that mediate these processes are not known. One method to id entify proteins potentially necessary for adhesion, spreading, and, thus, e ncapsulation is to use monoclonal antibodies that interfere with these func tions. In this paper, we report that a monoclonal antibody against Manduca sexta plasmatocytes effectively inhibited encapsulation of synthetic beads in vitro and in vivo. Furthermore, it inhibited plasmatocyte spreading in v itro. Other anti-hemocyte antibodies did not have these effects. The plasma tocyte-specific monoclonal antibody, mAb MS13, recognized a protein of appr oximately 90,000 daltons as indicated by Western blot analysis of hemocyte lysate proteins. The epitope recognized by mAb MS13 was present on the exte rior surface of plasmatocytes, Using indirect immunohistochemistry with hem ocyte-specific antibodies, we also determined that during encapsulation pla smatocytes were the first cells bound to latex beads and later layers consi sted of both plasmatocytes and granular cells. (C) 2001 Wiley-Liss, Inc.