Basic Functional Organization of the Immune System

The Immune System

  • The immune system is made up of a complicated network of barriers, cells, and soluble proteins that interact and communicate with one another. Based on the timing of their effects, the contemporary model of immune function is divided into three phases.
  • Skin and mucous membranes are examples of barrier defenses that act quickly to prevent pathogenic entry into human tissues. The innate immune response, which consists of a range of specialized cells and soluble substances, is quick but nonspecific.
  • The adaptive immune response is a slower but more specific and effective response that involves numerous cell types and soluble substances, but is principally directed by white blood cells (leukocytes) known as lymphocytes.
  • Blood cells, including all those involved in the immune response, emerge from hematopoietic stem cells in the bone marrow via several differentiation processes. 
  • Hematopoietic stem cells, unlike embryonic stem cells, are present throughout adulthood and allow for the continued differentiation of blood cells to replace those that have been lost due to age or function.

The Immune System – Immune Cells


  • B cells and T cells, the two most common types of lymphocytes, have the same morphology, with a big central nucleus surrounded by a thin coating of cytoplasm. Their surface protein identifiers, as well as the compounds they release, identify them from one another.
  • Although B cells mature in red bone marrow and T cells mature in the thymus, both originate in bone marrow. T cells mature in the thymus gland after migrating from the bone marrow. B and T cells can be found throughout the body, circulating in the bloodstream and lymph and residing in secondary lymphoid organs such as the spleen and lymph nodes.

B Cells

  • B cells are immune cells that produce antibodies as their primary activity. Antibodies are a type of protein that binds particularly to antigens, which are pathogen-associated compounds. An antigen is a chemical structure on a pathogen’s surface that interacts to antigen receptors on T and B lymphocytes.
  • B cells develop into cells that release a soluble form of their surface antibodies after being activated by antigen binding. Plasma cells are B cells that have been activated.

T Cells

  • The T cell, on the other hand, does not secrete antibody but is involved in the adaptive immune response in a variety of ways. Different T cell types can exude soluble molecules that communicate with other adaptive immune cells, or they can destroy cells infected with intracellular pathogens.

Plasma Cells

  • The plasma cell is another important lymphocyte type. A plasma cell is a B cell that has differentiated in response to antigen binding and obtained the ability to produce soluble antibodies as a result of this differentiation. 
  • The cytoplasm of these cells is densely packed with the protein-synthesizing machinery known as rough endoplasmic reticulum, which distinguishes them from regular B and T cells.

NK Cells

  • The natural killer cell, which is part of the innate immune response, is a fourth significant lymphocyte. A circulating blood cell with cytotoxic (cell-killing) granules in its vast cytoplasm is known as a natural killer cell (NK).
  • It shares this mechanism with the adaptive immune response’s cytotoxic T cells. NK cells are one of the body’s initial lines of defence in the fight against infections and cancer.

Further Readings