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Chapter 1 - The Immune System

The Immune Response Figure 1

Source: Dranoff G. Nat Rev Cancer 2004;4:11-22

The immune system comprises two arms functioning cooperatively to provide a comprehensive protective response: the innate and the adaptive immune system.

The innate immune system is primitive, does not require the presentation of an antigen, and does not lead to immunological memory.

Its effector cells are neutrophils, macrophages, and mast cells, reacting within minutes to hours with the help of complement activation and cytokines (CK).


The Immune Response Figure 2

Source: Kaiser Gary, Professor at the Community College of Baltimore County

The adaptive immune response is provided by the lymphocytes, which precisely recognise unique antigens (Ag) through cell-surface receptors.

Receptors are obtained in billions of variations through cut and splicing of genes and subsequent negative selection: self-recognising lymphocytes are eradicated.

Immunological memory after an Ag encounter permits a faster and heightened state of response on a subsequent exposure.


Lymphocytes develop in primary lymphoid tissue (bone marrow [BM], thymus) and circulate towards secondary lymphoid tissue (lymph nodes [LN], spleen, MALT).

The Ag reach the LN carried by lymphocytes or by dendritic cells. Lymphocytes enter the LN from blood transiting through specialised endothelial cells.

The Ag is processed within the LN by lymphocytes, macrophages, and other immune cells in order to mount a specific immune response.

Revision Questions

  1. What are the effector cells of the innate immune system?
  2. Which cells are responsible for immune memory?
  3. In which anatomical structure are the antigens processed by lymphocytes?
Introduction Immunoglobulins and B-Cell Development

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