MicrobiologyBytes: Infection & Immunity: Immune system Updated: July 12, 2005 Search

The Cells of the Immune System

Aims and Objectives

By the end of the module you should be able to:
  1. appreciate the common origin of the cells of the immune system from the bone marrow
  2. describe in simple terms the microscopic appearance of the cells of the immune system:
    B and T lymphocytes
    plasma cells
    dendritic cells
  3. describe in simple terms other effector cells such as:
    neutrophil polymorphs
    eosinophil polymorphs
    mast cells

The major cell types in the immune system are lymphocytes and phagocytic/dendritic cells.

1. Lymphocytes

There are two broad sub-types of lymphocyte. These are known as B cells and T cells. All of them are derived from the bone marrow but T cells undergo a process of maturation in the thymus gland. Mature lymphocytes all have a similar appearance. They are small cells with a deeply basophilic nucleus and scanty cytoplasm. B and T cells circulate in the blood and through body tissues. B cells give rise to plasma cells which secrete immunoglobulins (antibodies). T cells also respond to antigens. Some of them (CD4+) secrete lymphokines which act on other cells involved in the immune response. Others (CD8+, cytotoxic) are able to cause lysis of infected cells.

2. Macrophages and dendritic cells

These cells are derived from the bone marrow and have a variety of functions in the immune response:

The cells performing these various functions have differing microscopic appearances but they are grouped together as the mononuclear phagocytic system.

Polymorphs and mast cells are also involved in the effector side of the immune response.

Click on any of the cells below to identify the cell type and get further information:

© AJC 2007.