Immunology: Gene Expression and Natural Defense Systems
Learning Objectives: By the end of this chapter, you will understand the major defense systems of animals, the characteristics of nonspecific and specific immunity, humoral and cellular immune responses, antibody diversity, and immune system malfunctions.
Introduction to Animal Defense Systems
Every moment of every day, your body is under siege. Bacteria, viruses, fungi, and parasites constantly attempt to invade your tissues, seeking nutrients and a place to reproduce. Yet most of the time, you remain healthy. This remarkable feat is accomplished by your immune system—a complex network of cells, tissues, and organs that has evolved over millions of years to protect animals from pathogens.
The immune system operates through multiple layers of defense, each with distinct mechanisms and characteristics. Understanding these systems is fundamental to medicine, as immune dysfunction underlies conditions ranging from common allergies to life-threatening autoimmune diseases and immunodeficiencies.