Biology 107
Lecture Notes: Defenses against disease II.
Reading:
Chapter 43 in text.
The immune response
The body will mount either a humoral response or a
cell-mediated response, depending on the antigen which stimulates the system
Helper T lymphocytes function in both humoral and cell-mediated immunity
- antigen
presenting cells (APCs).
- Helper
T cells that bind to a class II MHC-antigen complex on an APC are induced
to differentiate into either of two clones of cells
In the cell-mediated response, cytotoxic T cells (Tc
cells) defend against intracellular pathogens
- Tc
cells have receptors that bind to antigen-class I MHC complexes (note that
this differs from T helper cells which bind to antigen-class II MHC
complexes)
In the humoral response,
B cells produce antibodies against extracellular pathogens
The selective activation of a B cell results from one of two
mechanisms:
á T-dependent
antigens
á T-independent
antigens
Antibody structure and function
- Antigens
are usually proteins or large polysaccharides that make up a portion of
the outer covering of pathogens or transplanted cells
- Antibodies
comprise a specific class of proteins called immunoglobulins (Igs)
- The
antigen-binding site is responsible for the antibodyÕs ability to identify
its specific antigen epitope and the constant regions are responsible for
the mechanism by which the antibody inactivates or destroys the antigenic
invader
á
Antibody-mediated disposal of antigen
o Neutralization
o opsonization
Acquired
immunodeficiency syndrome (AIDS)
- AIDS
is a severe immune system disorder caused by infection with the human
immunodeficiency virus (HIV)