The Biology Project: Immunology

Immunology Problem Set

Problem 4: Adaptive immune response

Tutorial to help answer the question:

___________ are responsible for the production of antibody against free pathogens and soluble products from pathogens while ____________ destroy pathogen and virally infected cells and abnormal cells.

A. Cytotoxic T cells, B cells
B. Macrophages, T cells
C. B-cells, helper T cells
D. B-cells, cytotoxic T cells


Adaptive immune response

The innate system is directed against any pathogen. If an invading pathogen escapes the innate defenses, the body can launch an adaptive, or specific response against one type of antigen. The adaptive immune response is divided into two systems:

  • Humoral system
  • Cellular system

The humoral system makes antibodies to eliminate pathogen and their products. The cellular system eliminates pathogens that have invaded cells and regulates the body's entire immune response.

Humoral system

B cells are specialized white blood cells produced in the bone marrow. Each B cell contains multiple copies of one kind of antibody as a surface receptor for antigen. The entire population of B cells has the ability to specifically bind to millions of different antigens.
When the antibody on the surface of a B cell binds to an antigen, the cell can be stimulated to undergo proliferation and differentiation. This process is called clonal selection. The cells produced make the same antibody, but become memory cells and plasma cells. Memory cells insure that subsequent infections by the pathogen receive a more rapid response. Plasma cells secrete large amounts of the antigen-specific antibody. T helper cells, part of the cellular system, are usually required for the clonal selection of B cells. Antibody secreted by plasma cells forms complexes with free pathogens and their toxic products. The complexes can inactivate pathogens and stimulate other innate systems including phagocytic cells and complement to eliminate the danger from our extracellular fluids.

Cellular system

Some pathogens can escape antibody detection by infecting cells. Cells containing pathogen display antigen fragments on their cell surfaces. Receptors on the surface of cytotoxic T cells (called CD8 cells) can detect the presence of pathogen specific antigen fragments and activate a killing response (apoptosis) that leads to the death of the infected cell. Cytotoxic T cells must interact with helper T cells (CD4 cells) to regulate destruction of infected cells. Helper T cells regulate other cells of the immune system through secretion of molecules called cytokines.
Microscopic movie of cytotoxic
T cells killing a tumor cell
(1257 kb)


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