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| Author(s): |
Anete Pedro Lourenço
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Ribeirão Preto. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC) |
| Defense date: | 2008-01-11 |
| Examining board members: |
Zila Luz Paulino Simoes;
Angel Roberto Barchuk;
Iscia Teresinha Lopes Cendes;
Sirlei Daffre;
Maria Luisa Paco Larson
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| Advisor: | Zila Luz Paulino Simoes |
| Abstract | |
Insects have developed an efficient immune system against parasites and pathogens, which is comprised of both cellular and humoral responses. The cellular mechanisms involve phagocytosis and encapsulation by hemocytes, whereas the humoral responses include activation of prophenoloxidase and synthesis of antimicrobial peptides by the fat body, which are released into the hemolymph. Two signaling pathways, Toll and Imd, control the expression of genes encoding antimicrobial peptides. Genome-wide analyses of the honey bee, Apis mellifera, have identified predicted genes for these signaling pathways. However, immune response mechanisms in honey bees were not yet in depth studied. We analyzed the transcription of effector genes (abaecin, hymenoptaecin, defensin, transferin, prophenoloxidase), as well as other immune genes, such as pathogen recognition genes (PGRP, GNBP) and signaling genes (cactus, relish, dorsal 1- B). We also investigated the role of the storage proteins Vitellogenin, Hexamerin 70a, Lipophorin I/II and Lipophorin III in the honey bee immunity. Finally, we analyzed the effect of nutrition and aging on honey bee immunity. Gene expression of signaling pathway components was assessed in honey bees that had been infected with the bacteria Serratia marcescens or Micrococcus luteus through injection or oral challenge. Honey bees infected with these microorganisms had strong up-regulation of antimicrobial peptide genes and of transferin, and also other changes in transcript abundance after 3 and 12 hours of challenge. The roles of prophenoloxidase and dorsal in the immune response, described as genes encoding important proteins in other insects, were also investigated. In this case we used RNA interference (RNAi) to silence the expression of these genes. RNAi efficiently silenced the target genes. However, injection of doublestranded RNA in honey bees induced a reaction by the immune system. This made it difficult to determine the role of prophenoloxidase in honey bee immunity. Yet, silencing of dorsal and its isoforms led us to consider dorsal 1-A or dorsal 2 as members of the signaling pathways that produce antimicrobial peptides, especially defensin. The abundance of storage proteins transcripts and proteins was lower in infected bees than in controls, giving evidence that these proteins participate in the immune process in honey bees. Moreover, protein consumption caused up-regulation of genes encoding storage proteins, which may favor the maintenace of the immune response capacity. The effect of aging on decline in immunity was analyzed in (young) nurse bees and (old) foragers from normal free-flying colony. We also examined bees from a single-cohort colony, in which all individuals were at the same age; but some were nursing, while others were foraging. All the bees, independent of age or behavior, were able to activate the immune system after infection with S. marcescens. However, foragers, independent of age, were always more susceptible to infections than were nurse bees. This is probably due to physiological differences between bees, which confers to the nurses more competence to survivorship. (AU) | |