Innate Immunity

From Louis Pasteur to Jules Hoffmann

Yves Carton

• Publisher: ISTE Press - Elsevier
• Year: 2019
• ISBN:
  9780128218105
• Topic: Medizin
• Subtopic: Immunologie

Innate immunity is a new branch of immunology, confirmed by three Nobel Prize winners in 2011. It is the first line of defense against pathogens and is in a way the preliminary step of adaptive immunity which occurs later, and only present in vertebrates.

This book examines the way in which innate immunity was discovered in invertebrates. As a starting point, it looks at the work of Louis Pasteur on silkworm disease and the findings of Ilya Metchnikov, discoverer of phagocytosis. It also investigates André Paillot, who in 1920 demonstrated the existence of humoral immunity in insects, unrelated to the type of immunity that was initially thought to be present in all vertebrates.

Finally, Innate Immunity shows how the group directed by Jules Hoffmann found strong similarities between the innate immunity response of insects and mammals. The discovery of a receptor protein in Drosophila, which is also found in humans, was what led to Jules Hoffmann being awarded the Nobel Prize in 2011.

• Presents the transformations experienced by the domains of innate immunity
• Shows the lineage of these results
• Bridges the gap between innate immunity of invertebrates and that of vertebrates

1

Louis Pasteur and Silkworm Disease (1865–1870)

Abstract

Louis Pasteur (1822–1895) was the first scientist to pursue the nascent science of bacteriology of bacteriological science (i.e. the study of bacteria), with many of these cases the first reared attempts to isolate the origins of diseases. However, before totally devoting himself to contagion affecting animals (chicken cholera, sheep anthrax) and the process of contamination, as well as those affecting humans (rabies), Pasteur led an investigation into the causes of a disease that affected silkworm farms, particularly in southern France, and to provide a cure. This disease probably appeared as early as 1843, dividing silk production by four between 1855 and 1865.

Keywords

Beauveria bassiana; Developmental cycle; Microsporidia; Microsporidium cycle; Pebrine; Silkworms; Streptococcus bombycis; Villa Vicentina

1.1 Introduction

Louis Pasteur (1822–1895) was the first scientist to pursue the nascent science of bacteriology of bacteriological science (i.e. the study of bacteria), with many of these cases the first reared attempts to isolate the origins of diseases. However, before totally devoting himself to contagion affecting animals (chicken cholera, sheep anthrax) and the process of contamination, as well as those affecting humans (rabies), Pasteur led an investigation into the causes of a disease that affected silkworm farms, particularly in southern France, and to provide a cure. This disease probably appeared as early as 1843, dividing silk production by four between 1855 and 1865¹.

This work, spread over five years (1865–1870), I would divert Pasteur from his innovative work on fermentations. However, this research would prove to be, for him, a real “biological” lesson of what he would also develop, concerning later notions – that were new for the time – of pathogens, infection, contagion and “hereditary” transmission.

In 1865, at the request of the French government, Pasteur took an interest in silkworm disease, with the obligation to travel to the territory concerned. In fact, he was approached by his former university mentor, Professor Jean Baptiste Dumas (1800–1884), a renowned chemist and former French Minister of Agriculture and Trade. At that time, he was a senator in the Gard, a French department in southern France where this disease was rampant: he wanted to find a cure for this disease and considered his former student to be the right man for the job. Pasteur was, at that time, a highly appreciated researcher, particularly for his work on fermentations, which he developed during his stay in Lille as Dean of the Faculty of Science at the new university. It is important to understand the nature of his discovery: contrary to the ideas of the time (supported in particular by the famous professor of the University of Giessen, J. von Liebig (1803–1873), who saw fermentation as a simple catalytic process caused by a ferment). Pasteur totally opposed this conception, recognizing that yeast had a fundamental role in fermentation. As a chemist, Pasteur discovered the presence of yeast using the new achromatic microscope: fermentation was indeed the work of living organisms. At the end of the century, these two antagonistic positions could be reconciled: yeast is indeed a living organism, which produces a molecule, the ferment (an enzyme), but it is the latter that induces a chemical reaction. In fact, Pasteur discovered in these fermentation processes the role of various yeasts, as well as of bacteria (butyric fermentation). He was undeniably the father of bacteriology. It is, therefore, surrounded by these discoveries, that Dumas wanted to entrust him with this mission to fight against the silkworm disease. He was a little disconcerted by this request, alleging that he had never seen a silkworm caterpillar or its cocoon in his life!

Figure 1.1 Fifth-instar silkworm caterpillar, the species Bombyx mori, on a branch of mulberry leaves, the only plant on which this species feeds (source: © Pasteur L., Etudes sur la maladie des vers à soie, tome 1, la pébrine et la flacherie, ed. Gauthier-Villars, Paris, 1870). For a color version of this figure, see www.iste.co.uk/carton/innate.zip

For five years, from 1865 to 1869, Pasteur stayed in the town of Alais, Gard (today known as Alès). Concerning his research work, Pasteur reported to the Académie des sciences (French Academy of Sciences), in the form of 21 communications or letters, published from 1865 to 1870. We wanted to use this published scientific work to reconstruct his approach to the problem, his scientific path with his mistakes, and understand how a “chemist” could identify and solve a biological enigma that had previously confused many scientists, French or foreign.

1.2 Current knowledge about silkworms and pebrine disease

Silkworm farming, which began in Turkey in AD 552 (two monks fraudulently brought the graine, i.e. the silkworm eggs of this butterfly, from Tibet), has developed in Europe, mainly in Andalusia (Spain) and Italy. This presupposes that the mulberry tree – the only plant on which the caterpillar feeds – has also been cultivated. It was Olivier de Serres (1539–1619), an agronomist, who truly established the mulberry crop in France, hoping that this industry would bring more activities to the French regions, and freely France from a reliance on external suppliers of silk. The breeding of silkworms (called éducation in French) then developed on a wide scale in France, in specialized structures in silkworm farms. The development cycle from egg to adult lasts about 50 days. The five instar larvae (separated by four molts) develop over 30 days, ending with the “migration” of the caterpillar on the heather shoots (which have been deposited for this purpose), weaving its cocoon and transforming into a pupa. The adult butterfly emerges after 20 days. For the production of cocoons and their shipment to the spinning manufactures, they are boiled to kill the pupae.

Pebrine is a disease found in the silkworm, Bombyx mori (Lepidoptera), caused by the microsporidium Nosema bombycis, with a poorly defined taxonomic status, but with similarities to fungi. The genus Nosema, described in 1857 by Professor von Nägeli of the University of Zurich, includes 32 species, all parasites of Insects and various arthropods. This disease – with no apparent symptoms at the beginning of contamination – results at an advanced stage, in small black spots on the skin of the caterpillar, as well as on the butterfly, which has the appearance of peppercorns. First called “maladie de la tache” (silkworm spot disease), Armand de Quatrefages² (1860a) gave the name pebrine to this disease, referring to peppercorns, whose name in Provençal dialect is pebre.

Figure 1.2 A sick silkworm caterpillar: the characteristic black spots of the disease (pepper in Provencal dialect is pèbre, hence the name of the disease, pebrine, given by de Quatrefages) (source: © Pasteur L., Etudes sur la maladie des vers à soie, tome 1, la pébrine et la flacherie, ed. Gauthier-Villars, Paris, 1870). For a color version of this figure, see www.iste.co.uk/carton/innate.zip

Figure 1.3 Appearance of the spots under the cuticle of a sick caterpillar (source: © de Quatrefages A., Etudes sur les maladies actuelles du wor à soie, Comptes rendus de l Académie des Sciences, XXX, 1860a)

Figure 1.4 Life cycle model of Nosema bombycis (source: text and drawing by C. Wang Jian-Yang, PhD 2007, with the kind permission of C. Texier, Clermont-Ferrand University)

The life cycle of N. bombycis is divided into the environmental (infective) phase and intracellular phases (merogony and sporogony). All stages of development of N. bombycis are diplocaryotic. (1). In the environmental infective phase, the proper environmental conditions are required to active mature spores, resulting in polar tube extrusion and sporoplasm deposition into the host cell cytoplasm. (2). In the intracellular phases, N. bombycis sporoplasm is in direct contact with the host cell cytoplasm and matures into meront, which multiplies by binary fission (merogony). The plasmalemma thickening is the beginning of the sporogony stage. Each sporont produced two sporoblasts, and each sporoblast produced two mature spores (sporogony). (3). Spore dimorphism: N bombycis completes its relatively simple life cycle with two sporulation sequences forming two types of spore respectively: “primary spore, internal spore or FC (few coils of polar filament) spore”, which can germinate quickly after formation (autoinfection) and “environmental spore or external spore” (N, nuclear; PT, polar tube)³.

The microsporidium cycle⁴ includes an infectious phase in the surrounding environment and an intracellular phase in the silkworm. The infectious phase is represented by spores, which, in contact with the caterpillar stage of the Insect, will germinate, releasing a polar tube that penetrates into directly accessible cells: the epidermis located under an abraded cuticle, the middle intestine and the deep part of the tracheoli (the terminal tracheal cells): the silk gland, Malpighi tubes, the nervous system, the dorsal vessel and gonads. This leads to systemic, i.e. generalized, auto-infection. At the end, i.e. at the death of the caterpillar, the spores formed will be released into the external environment. Here is a very brief summary of the cycle of this microsporidium. On the other hand, organs with an external cuticle, the trachea (which is an invagination of the epidermis, therefore bordered by a cuticle), the anterior and posterior intestines (bordered by a cuticle) and the chitinized parts of the mouth cannot be infested.

The spore, once germinated (sporoplasm) in the potentially attackable cells, each generates a meront, which by binary fission, gives two sporonts. Each of its sporonts divides again twice, giving successively two sporoblasts and four mature spores, in each infested cell. Each of these mature spores can then infest a new cell with its germline tube. These various stages are all diplokaryotic, i.e. they have t...