title: Isolation and identification of a plasmatocyte-spreading peptide from the hemolymph of the lepidopteran insect Pseudoplusia includens.
abstract: Insect blood cells (hemocytes) play an essential role in defense against parasites and other pathogenic organisms that infect insects. A key class of hemocytes involved in insect cellular immunity is plasmatocytes. Here we describe the isolation and identification of a peptide from the moth Pseudoplusia includens that mediates the spreading of plasmatocytes to foreign surfaces. This peptide, designated plasmatocyte-spreading peptide (PSP1), contains 23 amino acid residues in the following sequence: H-ENFNGGCLAGYMRTADGRCKPTF-OH. In vitro assays using the synthetic peptide at concentrations >/=2 nM induced plasmatocytes from P. includens to spread on the surface of culture dishes. Injection of this peptide into P. includens larvae caused a transient depletion of plasmatocytes from circulation. Labeling studies indicated that this peptide induced 75% of plasmatocytes that were double-labeled by the monoclonal antibodies 49G3A3 and 43E9A8 to spread, whereas plasma induced significantly more plasmatocytes to spread. This suggests that only a certain subpopulation of plasmatocytes responds to the peptide and that other peptidyl factors mediate plasmatocyte adhesion responses.
authors.affiliation: Department of Entomology, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: K D
authors.initials: KD
authors.lastname: Clark
authors.forename: L L
authors.initials: LL
authors.lastname: Pech
authors.forename: M R
authors.initials: MR
authors.lastname: Strand
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001681:Biological Assay; D002448:Cell Adhesion / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006434:Hemocytes / Q000187:drug effects / Q000502:physiology*; D006458:Hemolymph / Q000737:chemistry*; D036341:Intercellular Signaling Peptides and Proteins; D007915:Lepidoptera / Q000737:chemistry*; D008969:Molecular Sequence Data; D010452:Peptide Biosynthesis; D010455:Peptides / Q000302:isolation & purification / Q000494:pharmacology; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C108084:plasmatocyte-spreading peptide 1