| Encapsulation, an important cellular immune response in insects, involves a series of adhesion events by hemocytes. One class of hemocytes, the granulocytes, adheres to the target first and is involved in recognition of foreignness. Another class of cells, the plasmatocytes, then adheres to the target and each other, in forming a multicellular capsule. Finally, the adhesion of a single layer of granulocytes results in the termination of capsule growth. The receptors that mediate these adhesion events have not been identified. I have studied the process of encapsulation in a noctuid lepidopteran, Pseudoplusia includens, in an attempt to better understand the mediators of hemocyte adhesion.; Studies of in vitro encapsulation of a variety of abiotic targets did not reveal a narrowly defined set of target characteristics that predicted encapsulation. However, these studies did demonstrate that recognition can proceed by two separate mechanisms, depending on the specific target: recognition by granulocytes, or recognition by as yet uncharacterized hemolymph-soluble opsonins. Ligand binding studies with granulocytes indicate that they specifically possess scavenger receptor-like molecules. Scavenger receptors are a class of promiscuous receptors known to be important in mammalian immune responses, and thus could be important as mediators in granulocytes of processes such as non-self recognition.; I also isolated representatives of integrins, another class of heterodimeric adhesion receptors, from hemocytes. I cloned three alpha and one beta subunit from hemocyte DNA. Northern blot analysis showed all four subunits are expressed in granulocytes, and three of the four in plasmatocytes. Examination of transcription patterns using real-time PCR showed a strong positive correlation with cell adhesion and encapsulation for one of the alpha subunits, suggesting a specific role in maintenance of cell adhesion and capsule integrity. |
