Meet the editors

Dr. Ortega-Villaizan obtained a degree in Biological Sciences from the University of Alicante, Spain, in 1995, and a Ph.D. in Agricultural Sciences (Fish Population Genetics) at the University of Tohoku, Japan, in 2005. In her postdoctoral period, she began working as a researcher at the Institute of Research, Development, and Innovation in Healthcare Biotechnology in Elche (IDiBE), University Miguel Hernandez (UMH), Spain.

Dr. Ortega-Villaizan was working as a postdoctoral researcher in what would be her current research line, which is the search of therapies and prophylactics against viral pathologies in aquaculture, specifically in the context of the fish immune response. In 2014, she was granted an ERC Starting Grant, which commenced in 2015 at the IDiBE-UMH. Dr. Ortega-Villaizan was leading her own laboratory to investigate the crosstalk between red and white blood cells in the context of viral infections and DNA vaccine immunizations to elucidate the role of red blood cells in the fish immune response. Since 2018, she has been an assistant professor in the Department of Biochemistry and Molecular Biology, UMH. Her current research interests are the red blood cells of fish and their involvement in fish immune response and as target cells in the search for therapies or prophylactics against fish viral infections.

Dr. Chico obtained a degree in Biology at the University of Alicante, Spain, in 2003, and a degree in Biochemistry at Miguel Hernandez University (UMH), Spain, in 2005. She acquired a Ph.D. in Molecular and Cell Biology with a focus on Fish Immunology and Viral Prophylaxis at the Institute of Research, Development, and Innovation in Healthcare Biotechnology in Elche (IDiBE), University Miguel Hernandez (UMH), Spain

in July 2010. In 2012, she began working as a postdoctoral researcher at the Department of Organism Biology and Comparative Physiology, Uppsala University, Sweden. Her work was focused on innate immunity and hematopoiesis in crustaceans. Since 2015, Dr. Chico has been a postdoctoral researcher at the IDiBE-UMH, Spain. She works with Dr. Maria del Mar Ortega-Villaizán's research group at the IDiBE´s research subgroup of Antiviral and Antimicrobial Strategies. Her current research interest is the evaluation of the innate and adaptive immune response to viral pathogens in aquaculture in the context of the role of red blood cells as cell mediators in the fish immune response.

Contents

**Preface XI**

**Acknowledgments XV**

**Chapter 1 1**

**Chapter 2 23**

**Chapter 3 39**

**Chapter 4 53**

**Chapter 5 75**

Immune System of Fish: An Evolutionary Perspective

Role of Kupffer Cells in Systemic Anti-Microbial Defense

*by Lixing Huang, Rongchao He, Youyu Zhang and Qingpi Yan*

Metabotropic Receptors 4 and the Immune Responses

*by Hiroyuki Nakashima, Masahiro Nakashima, Manabu Kinoshita* 

The Role of the Aryl Hydrocarbon Receptor (AhR) in the Immune

*by Faustina Pappoe and Samuel Victor Nuvor*

Response against Microbial Infections

*by Zhuoya Wan and Song Li*

with or without Medication

*and Shuhji Seki*

*by Sujata Sahoo, Husne Banu, Abhinav Prakash and Gayatri Tripathi*

Host-Microbial Relationship: Immune Response to Microbial Infections

## Contents


Preface

The environment comprises a variety of infectious microbial agents. Many of them can cause pathological disorders and even death in organisms exposed to them if they multiply uncontrollably. However, organisms can control infections caused by pathogens thanks to the existence of the immune system. The immune system is a set of biological processes that prevents an organism from infectious diseases [1]. In vertebrates, the immune system is divided into the innate and the adaptive immune systems. The innate immune system is the most ancient form of defense. It is the first mechanism to respond to infections and the main defense mechanism in invertebrates [2]. It is characterized as non-pathogen-specific and does not provide specific long-lasting immunity to the host [3]. The components of the innate system comprise the physical barrier (the skin), molecular effectors (complement system, antimicrobial peptides, and cytokines), and immune cells (granulocytes,

The innate immune system has certain specificity in the recognition of pathogens through pattern recognition receptors (PRRs). These receptors are expressed in many cell types, and they are strategically located throughout cells. PRRs are in cell membranes where they mediate recognition of extracellular pathogens, and in endosomes and cytoplasm where they detect intracellular pathogens. PRRs recognize small molecular motifs characteristic of pathogens called pathogen-associated molecular patterns (PAMPs) [4], which are conserved through evolution. There is a variety of PAMPs, for example, bacterial flagellin, bacterial lipopolysaccharides (LPS), peptidoglycans, or nucleic acid variants from viruses [double-stranded RNA (dsRNA) or nonmethylated viral 5'-C-phosphate-G-3′ (CpG)-containing DNA] [4]. The activation of PRRs with their PAMPs activates the signaling networks that modulate the expression of cytokines such as type I interferon and antiviral proteins

In addition, vertebrates possess the adaptive immune system, which consists of a specific immune response based on immune memory against recurrent pathogens [6]. B and T lymphocytes are principally responsible for the specificity of the adaptive immune responses [7]. This system is highly specific and can discriminate between self- and non-self-cells. Both the innate and adaptive immune systems do not act separately; they are completely integrated to protect the organism against

Nowadays, the immune system of higher vertebrates like mammals is being more studied in depth in comparison with the immune system of lower vertebrates such as teleosts. The immune system of teleosts is physiologically comparable to that of higher vertebrates, despite certain differences such as the fact that the main haematopoietic organ of teleosts is the head kidney, as they do not have bone

marrow (the main haematopoietic organ in mammals) [8]. Apart from that, teleosts possess a less complex adaptive immune system compared to higher vertebrates and therefore rely heavily on innate immune responses to face continuous pathogen attacks. Teleosts reside in extremely distinct environments from those in which mammalians have evolved, so it is not misbegotten that aquatic vertebrates have

monocytes, macrophages, and natural killer cells) [3].

to protect the organism against infections [5].

the attack of pathogens [1].
