Unresolved Questions

The role of chemical mediators in the cell-to-cell communication pathways required for successful immune responses as complicated as encapsulation have only just begun to be explored. Also, the initial signaling events that discriminate "nonself" at the most basic level remain remarkably obscure. This is particularly true for the recognition of eukaryotic parasites, which seem to use a complex mix of strategies such as host immunosuppression, antigen masking, and antigen mimicry to avoid being detected as foreign. Progress in identifying resistance and susceptibility genes in insect hosts, and the complementary virulence/avirulence genes in parasites has begun only recently, although efforts are intensifying to clarify these genetic components, particularly in Drosophila. Although insects lack "memory cells" in their immune system, some long-lived insects such as cockroaches exhibit an enhanced response to a secondary challenge, raising the possibility that insects can show a sensitization response, albeit via as yet unknown mechanisms. Although the antibacterial defenses of insects have been well characterized in the past two decades, even at the molecular level, the defenses mobilized by insects against invasion by viral pathogens are only now being delineated, despite intensive efforts to clarify mechanisms of antiviral resistence. In most species, the roles of hormones such as juvenile hormone and ecdysteroid in regulating immunity have yet to be deciphered. The prospect of developing transgenic insects expressing refractoriness-related traits offers promise of the ability to control disease transmission by insect vectors. Likewise, the prospects of genetic manipulation of agricultural pests to enhance their susceptibility to biopesticides, and to increase the virulence of the pathogen, offer great promise to agriculture. Clearly, many challenging questions need to be addressed to decipher the tactics of parasite/pathogen offense and host defense.

See Also the Following Articles

Genetic Engineering • Hyperparasitism • Pathogens of Insects Further Reading

Beckage, N. E. (1997). The parasitic wasp's secret weapon. Sci. Am. 277, 50—55. Beckage, N. E. (1998). Modulation of immune responses to parasitoids by polydnaviruses. Parasitology 116, S57—S64. Beckage, N. E., Thompson, S. N., and Federici, B. A. (eds.). (1993). "Parasites and Pathogens of Insects": Vol. 1, "Parasites," Vol. 2, "Pathogens." Academic Press, San Diego.

Carton, Y., and Nappi, A. J. (2001). Immunogenetic aspects of the cellular immune response of Drosophila against parasitoids. Immunogenetics 52, 157-164.

Dimopoulos, G., Muller, H. M., Levashina, E. A., and Kafatos, F. C. (2001). Innate immune defense against malaria infection in the mosquito. Curr. Opin. Immunol. 13, 79-88. Gillespie, J. P., Kanost, M. R., and Trenczek, T. (1997). Biological mediators of insect immunity. Annu. Rev. Entomol. 42, 611-643. Hoffmann, J. A., and Reichhart, J. M. (1997). Drosophila immunity. Trends

Cell Biol. 7, 309-316. Hoffmann, J. A., Kafatos, F. C., Janeway, C. A., and Ezekowiltz, R. A. (1999). Phylogenetic perspectives in innate immunity. Science 284, 1313-1318.

Gupta, A. P. (ed.). (1991). "Immunology of Insects and Other Arthropods."

CRC Press, Boca Raton, FL. Imler, J. L., and Hoffmann, J. A. (2001). toll Receptors in innate immunity.

Trends Cell Biol. 11, 304-311. Paskewitz, S. M., and Gorman, M. J. (1999). Mosquito immunity and malaria parasites. Am. Entomol. 45, 80-94. Pathak, J. P. N. (ed.). (1993). "Insect Immunity." Kluwer Academic

Publishers, Dordrecht, Netherlands. Schmidt, O., Theopold, U., and Strand, M. (2001). Innate immunity and its evasion and suppression by hymenopteran parastioids. Bioessays 2,

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