Insect Immunology

Nancy E. Beckage, Nancy E. Beckage

• Editorial: Academic Press
• Año: 2011
• ISBN:
  9780080556338
• Categoría: Medicine
• Categoría: Immunology

This work is the first book-length publication on the topic of insect immunology since 1991, complementing earlier works by offering a fresh perspective on current research. Interactions of host immune systems with both parasites and pathogens are presented in detail, as well as the genomics and proteomics, approaches which have been lacking in other publications. Beckage provides comprehensive coverage of topics important to medical researchers, including Drosophila as a model for studying cellular and humoral immune mechanisms, biochemical mediators of immunity, and insect blood cells and their functions.

• Encompasses the most important topics of insect immunology including mechanisms, genes, proteins, evolution and phylogeny
• Provides comprehensive coverage of topics important to medical researchers including Drosophila as a model for studying cellular and humoral immune mechanisms, biochemical mediators of immunity, and insect blood cells and their functions
• Most up-to-date information published with contributions from international leaders in the field

1

INSECT AND VERTEBRATE IMMUNITY: KEY SIMILARITIES VERSUS DIFFERENCES

OTTO SCHMIDT^*, ULRICH THEOPOLD^** and NANCY E. BECKAGE^†, ^*Insect Molecular Biology, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond, SA 5064, Australia; ^**Department of Molecular Biology and Functional Genomics, Stockholm University, S10691 Stockholm, Sweden; ^†Departments of Entomology and Cell Biology and Neuroscience and Center for Disease Vector Research, University of California-Riverside, Riverside, CA 92521, USA

ABSTRACT

Historically, the mammalian adaptive immune system was the first to be analyzed in depth, providing strong paradigms on mechanisms of immune recognition and the distinction of self and non-self. However, the differentiation power of the innate immune system and the possible diversity of defense devices emerging in non-mammalian organisms may offer new perspectives on how multicellular organisms recognize potentially damaging objects or substances.

Chapter Outline

1.1. Introduction

1.2. Similarities

1.2.1. Sensing Mechanisms

1.2.2. Effector Mechanisms

1.3. Differences

1.3.1. Acquired (Adaptive) Immune System in Higher Vertebrates and Immunological Memory Involving Clonally Selected Antibody-Producing Cells

1.3.2. Inducible Tolerance and Memory in Invertebrates

Abbreviations:

LM =

leverage mediated

LPS =

lipopolysaccharide

MHC =

major histocompatibility complex

PAMP =

pathogen-associated molecular patterns

PAMS =

pathogen-associated molecular structures

RNAi =

RNA interference.

1.1 INTRODUCTION

Insects are a large and diverse group of animals that have adapted to extreme environments, including endoparasitic lifestyles, where one insect develops inside another insect. Compared to insects, with more than 32 orders, some containing hundreds of thousands of species, vertebrates are a relatively small group and rather homogeneous in morphology and physiology. Nevertheless, higher vertebrates have evolved a unique defense system in the form of an anticipatory immune response in addition to the innate immune system, which is common to all animals. The adaptive immune system is developed during early mammalian ontogeny, where gene rearrangements create thousands of gene variants encoding a repertoire of binding proteins that are clonally selected against self-recognition in immune-specific cells. After induction by foreign immunogens, a process which requires the involvement of the innate arm of the immune system, immune cells remain in readiness for future encounters with a potentially damaging object or dangerous substance.

While the adaptive immune system has impressive features involving the ontogenetic generation of antibody diversity and immunological memory, we have only started to analyze the differentiation power of the innate recognition system in vertebrates (Vivier and Malissen, 2005). Likewise, given the broad range of extreme and challenging environments in which some invertebrates live (Loker et al., 2004), we have not yet grasped the possible diversity of defense devices that may exist in non-mammalian organisms (Little et al., 2005). Comparisons of immune genes among related insect species (Drosophila and Anopheles) belonging to the same order of Diptera suggest very different defense strategies, using different protein families as recognition proteins and receptors (Christophides et al., 2004; Zdobnov et al., 2002). While immune strategies in most invertebrates remain to be analyzed, some already reveal highly specific and effective defense mechanisms that rival those of higher vertebrates.

Historically, the mammalian adaptive immune system was the first to be analyzed in depth using molecular biology tools. This has provided strong conceptual paradigms on how we perceive the mechanisms of immune recognition and the distinction of self and non-self. In fact, the notion that the specificity of immune recognition is determined exclusively by the nature of protein–epitope interactions has emerged from the formative power of antibody–antigen interactions that are highly specific and crucial for the immune response in specific immune cells. It is only recently that cell-free defense reactions uncovered multi-protein complexes upstream of cellular receptors (Schmidt and Theopold, 2004) that are relevant to recognition processes in insects. For example, cellular uptake reactions may be based on multi-protein complexes with enhanced detection capabilities due to combinatorial interactions between phagocytic receptors (Stuart and Ezekowitz, 2005) and upstream regulatory processes (Rahman et al., 2006). While these regulatory cascades were known to exist in many animal species (Krem and Cera, 2002), their relevance to insect immunity (Lemaitre et al., 1996) and development (Anderson, 2000) was uncovered first in Drosophila.

Another consequence of the conceptual preeminence of the adaptive immune system is the habit of some immunologists to use particular mammalian gene functions synonymous with general immune functions. Such is the strength of the mammalian paradigm that the presence of major histocompatibility complex (MHC) genes is sometimes correlated with the functionality of histocompatibility and the absence of MHC-like genes in other organisms is taken as evidence that these mechanisms do not exist in those organisms. But histocompatibility has been shown to be performed in many multi-cellular organisms, such as sponges (Fernandez-Busquets et al., 2002; Muller and Muller, 2003) or primitive chordates (De Tomaso et al., 2005) as part of a self-recognition mechanism, using different sets of proteins to achieve it (Litman, 2005).

In this chapter we use a comparison between insect and higher vertebrate immune reactions to highlight some of the progress that has been made in our understanding of how innate immune recognition has evolved to protect multicellular organisms against potentially damaging organisms. This also provides an opportunity to remind us of the large gaps that exist in our basic conceptual framework of how biological recognition processes work, particularly when it comes to the integration of immune functions with developmental and basic cellular functions, such as recognition of self.

1.2 SIMILARITIES

1.2.1 SENSING MECHANISMS

1.2.1.1 Recognition of Pathogen-Associated Molecular Structures

Biological recognition processes are generally perceived to be performed exclusively by the specific interactions of proteins with molecular structures that indicate non-self or altered-self. For example, the binding properties of antibodies, enabling the variable binding domains to attach to almost any molecular structure (antigens) and the ontogenic elimination process of self-binding antibodies by clonal selection, allow higher vertebrates with adaptive immune systems to signal non-self structures (Boehm, 2006; Mak and Saunders, 2006). Likewise, the evolution of specific binding proteins that interact with protein, lipid or sugar determinants (epitopes) that are unique to other organisms, identifies potentially damaging organisms in plants (Jones and Dangl, 2006) and animals (Janeway and Medzhitov, 2002). Since the innate immune system lacks clonal elimination mechanisms of self-binding proteins, the distinction between self and non-self relies on the selective accumulation of recognition protein repertoires that bind to target sites that are diagnostic for potentially damaging organisms (Janeway, 1989). These pathogen-associated molecular patterns (PAMPs) (Janeway, 1989) or pathogen-associated molecular structures (PAMSs) (Beutler, 2003) were selected in host organisms as target sites for potential recognition proteins. Thus, the distinction between self and non-self is based on the absence of microbe-specific structures in the host. A precondition for microbe-specific recognition by a host organism is that these struct...