Hemocytes from adult, female Aedes aegypti, intrathoracically inoculated with microfilariae (mf) of the nematode Dirofilaria immitis, were compared to saline-inoculated and uninoculated controls using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), 125I-labeling, and wheat germ agglutinin (WGA) binding techniques. Activation of wound healing and/or melanotic encapsulation responses by the inoculation of saline or mf into the host hemocoel induced alterations in the hemocyte activity of these mosquitoes. Protein assays of whole hemocyte lysates revealed that hemocytes from saline- and mf-inoculated mosquitoes had higher protein concentrations than uninoculated controls. Many polypeptides were seen within all three hemocytes preparations when stained with silver nitrate, but there was an overall increase in protein synthesis in hemocytes from inoculated mosquitoes. In addition, a 200-kDa polypeptide was uniquely expressed in hemocytes from inoculated mosquitoes. There were several prominent surface proteins labeled with 125I, and several of these increased dramatically in intensity during wound healing and/or a melanotic encapsulation response. Similar results were seen in two-dimensional separations. A set of basic polypeptides comigrated with an acidic polypeptide resulting in a surface protein of approximately 80-90 kDa that increased in inoculated mosquitoes. Hemocytes from inoculated mosquitoes exhibited a group of three acidic polypeptides, whereas hemocytes from uninoculated mosquitoes exhibited only one of these protein fragments. Three surface polypeptides bound 125I-labeled WGA, and binding of WGA to hemocyte surface polypeptides was successfully inhibited by the incubation of cells with the lectin and its competing sugar.