Biol 61 – The Immune System
The immune system functions to defend the body from invaders, including bacteria, viruses, and fungi, but it also
fights eukaryotic parasites and cancer cells as well.
The cells that are involved in the immune response are called
leukocytes = white blood cells (they are really colorless), in contrast to erythrocytes = red blood cells.
There are 3
parts to the defense of the body:
specific (acquired) immunity
1) passive defense
This includes skin (tough & resistant with a dead outer layer that makes it tough to infect), the
stomach (acidic and unfriendly to many things that might end up there), and mucus membranes (sticky to help
capture pathogens, agents of disease) in the sinuses and lungs, for example.
You also make defensive proteins
like lysozyme in your tears (this protein attacks bacterial cell walls).
2) non-specific immunity
This includes the action of the phagocytic cells
, ameoba-like cells that eat anything that
is not recognized as self, and the “complement
These are called “non-specific” responses because in
this type of response the immune system is not reacting to any “specific” type of pathogen (a specific virus like
a rhinovirus or rubella, for example), but is reacting to the presence of any kind of invader (any type of bacteria
or virus will be attacked this way).
3) specific immune response
This occurs when the body develops an immunity to specific pathogens (a particular
species of bacteria or strain of virus), and it involves white blood cells called
B cells (T
With the specific immune response, once you get infected your body
remembers how to fight that specific pathogen the next time you are infected.
We’ve basically already discussed the key features of passive defense, so let’s discuss
in a little more depth.
Phagocytic cells, or phagocytes, use
to ingest their targets, and
this is how they get their name (Fig. 43.3).
The major types of phagocytes we will discuss include:
Macrophages are attracted to damaged cells and chemicals released by bacteria, and they
can squeeze through the capillary endothelium to get to damaged or infected tissues.
found associated with tissues of the immune system (lymph nodes, the spleen, etc.) and are also found
moving through the interstitial fluid between the cells of all your organs and tissues (see the picture of
loose connective tissue from Chapter 40).
They will recognize and eat a large range of objects, including
viruses, bacteria, fungi, cell debris, dust, whatever. They also can play an important role in the specific