Preface

Macrophages are potent innate immune cells. In 1882, Elia Metchnikoff first discovered them as phagocytes in starfish larvae and the water flea (*Daphnia*). This discovery revolutionized the field of immunology and gave birth to innate immunity. Before this discovery, researchers were mainly focused on adaptive immunity (B and T cells). Now, macrophages are considered the most plastic cells in the hematopoietic system. They are present in every organ and tissue, previously regarded as an immune privilege. For example, they are present in the testes, brain (microglia), and eye retina. The liver macrophages are called Kupffer cells. The advancement in the biology of macrophages has established their role in different areas of biology, including reproduction, embryonic development, regeneration, neurosciences, metabolism, immunity, infection, and inflammation.

Macrophage biology and its role in different biological processes are ever-changing due to advances in the field and new technologies. The book covers the role of macrophages in various areas of biology in health and disease.

The book opens with Section 1, "Introduction" which includes the introductory chapter describing essential aspects of macrophages in the male and female reproductive system, embryonic development, tissue or organ regeneration, neurological learning and behavioral mechanisms, and systemic metabolism. These functions of macrophages highlight their role beyond being innate immune cells.

Section 2, "Macrophages in Vertebrate Immunity", includes seven chapters. Each chapter in this section describes essential aspects of macrophages in vertebrate biology. For example, they play a crucial immune function in lower vertebrates, including teleost fish. Other chapters in the section describe the importance of macrophages (pulmonary) in acute and chronic lung inflammatory diseases, wound healing, and innate immunity, as well as their regulatory role in gastrointestinal muscle layers.

Section 3, "Macrophages in Parasitic Infections," describes the regulatory role of macrophages in parasitic infections. It focuses on macrophages and leishmaniasis (Kala-Azar), a protozoan parasitic infection most prevalent in developing countries, including India, Brazil, and South Africa.

Section 4, "Macrophages in Bacterial Infections," focuses on the role of macrophages in bacterial infections. This section includes two chapters. The first chapter describes the role of macrophages in bacterial periodontitis, and the second chapter describes their function in pulmonary tuberculosis. Both these diseases affect a large portion of the population worldwide. For example, periodontal diseases affect 20%–50% of the global population. Similarly, 1.5 million people worldwide died from tuberculosis in 2020. Tuberculosis is the 13th leading cause of death in the world.

Section 5, "Macrophages in Viral Infections," discusses the role of macrophages in viral diseases. It includes three chapters. The first chapter discusses macrophage polarization during viral diseases, and the second chapter discusses Ebola virus interaction with the innate immune system and the third chapter discusses Macrophages and HIV/AIDS Pathogenesis.

Section 6, "Macrophages in Neurological Diseases," includes one chapter that discusses the role of macrophages in different neurological disorders, including neurodegenerative diseases.

Section 7, "Macrophages in Breast Cancer," includes a chapter that discusses macrophages in triple-negative breast cancer, their imaging, and their translating applications.

Finally, Section 8, "Stem Cells-Derived Macrophages," includes one chapter that examines pluripotent stem cell-derived macrophages, their current applications, and future perspectives.

This book provides updated information for biomedical researchers working with macrophages in different conditions, including infections, regeneration, wound healing, neurosciences, cancer, and stem cell biology. It is a useful resource for researchers and scientists in the field.

> **Dr. Vijay Kumar, Ph.D.** Department of Interdisciplinary Oncology, School of Medicine, Stanley S. Scott Cancer Center, Louisiana State University Health Science Center (LSUHSC), New Orleans, LA, USA

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Section 1

Introduction

Section 1 Introduction

#### **Chapter 1**
