The Immune System

There are physical, chemical, and cellular defenses against invasion by viruses, bacteria, and other agents of disease.

During the early stages of an infection, there is an inflammatory response

During later stages, leucocytes produce immune responses

The first two lines of defense are called Innate Immunity

The last line of defense is called Acquired Immunity

Surface coverage - the first line of defense

Non-specific responses - the second line of defense

Macrophage destroying bacterial cells

Animation - the First Two Lines of Defense

The Immune System (Specific Responses) - the third line of defense

Types of cells involved in the immune system:

Each type of virus, bacteria, or other foreign body has molecular markers which make it unique

Thus, immunological specificity and memory involve three events:

(1) Recognition of a specific invader

(2) Repeated cell divisions that form huge lymphocyte populations

(3) Differentiation into subpopulations of effector and memory cells

Antigen-presenting cell - a macrophage which digests a foreign cell, but leaves the antigens intact. It then binds these antigens to MHC molecules on its cell membrane. The antigen-MHC complexes are noticed by certain lymphocytes (recognition) which promotes cell division (repeated cell divisions)

Molecular cues that stimulate lypmphocytes to create an immune response

T cells (Helper T cells and Cytotoxic T cells)

Cell-mediated immune response

B cells, Plasma Cells, and Antibodies

Antibody-mediated immune response


Summary of the Immune Response

The Clonal-Selection Theory

Scientific evidence showed early researchers:

To explain these patterns, researched developed the clonal-selection theory, whihc made several key claims about how the adaptive immune system works:

Secondary Immune Response - Memory

The History of Vaccinations

Edward Jenner (1749-1823)