3. Adaptive immunity and immune response. Immune system – the basis of the immune response. Anatomy and structure of the immune system – immune organs (primary and secondary), immune cells (populations, markers, and function), molecules (cytokines and antibodies), HLA genes, and their products.

Introduction

This topic covers adaptive (acquired) immunity and the structure of the immune system: its types and forms, the cells and organs involved and how T and B lymphocytes develop, antibodies (immunoglobulins), the T cell receptor, and the MHC (HLA) genes and molecules that present antigens to T cells.

The immune system: basic concepts

The immune system is a complex biological system in multicellular organisms designed to resist and defend against pathogenic microorganisms. It recognizes and tolerates self (the own body) and recognizes and rejects non-self (foreign agents). It aims to preserve genetic and antigenic integrity against foreign agents and altered self-cell antigens (e.g., in autoimmune diseases or tumours). It is composed of lymphoid organs and immune cells that defend the body against pathogens and malignancies.

• Innate immunity (natural resistance): rapid and non-specific defences, important in the first hours and days of infection. It consists of physical, chemical, molecular and cellular defences.
• Adaptive immunity (acquired immunity): slower but specific and memory-based. It provides long-lasting protection through immune memory and is crucial for recovery in severe infections.