Acquired humoral immune response of the large milkweed bug,Oncopeltus fasciatus (Dallas), to injected materials

The large milkweed bug, Oncopeltus fasciatus (Dallas) responded to a single injection of Pseudomonas aeruginosa (Schroeter) Migula vaccine with the elaboration of lytic substances that were demonstrated in vitro in the serum. These factors appear to be responsible for the increased resistance to bacterial infection acquired by O. fasciatus in response to vaccination. Both the acquired resistance and lytic substances were detected 4 hr after vaccination. They reached their maximum level by 24 hr and disappeared within 5 days. A weak transitory resistance to Pseudomonas infection and low titre of lytic substances could be provoked by the injection of heterologous substances. Normal insects inoculated with immune serum exhibited a resistance equal to that acquired by individuals to specific vaccine.The acquired lytic substances resisted exposure to 75°C, 1 N HCl, and 1 N NaOH for 1 hr and retained their activity after storage at −20°C for at least 6 months. They are associated with several of the proteins in electrophoretically fractionated serum, to which they appear attached, but retain their activity in the supernatant of immune serum that has had the protein precipitated by trichloroacetic acid. They are not antigenic for rabbits, nor do they affect the antigenicity of the normal serum proteins.