Immunity is a topic on which many have written dissertations and
books. Equally so, it could take pages and pages, to explain the
intricacies of antibodies, immunity, endotoxins, exotoxins, etc. I
would love to do so, but??I leave it to some simple explanations and
plenty of illustrative links. (I, myself, learn so much better with
You are on the right track here, audy5000g, but you can?t lump all
infectious diseases together. If I understand you correctly, you say
that an organism enters through the nose/mouth, then the ?invaders
reaches our gut? , and then ?final stage is the skin rash, where the
body eliminates it?. This is not quite how it works.
I?ll describe several scenarios, simply, then below, add links to
sites that will illustrate and explain, in greater detail.
In cellular immunity, infectious agents are destroyed by
macrophages, specialized white blood cells (WBC), called T-cells. The
cells ?eat? the organisms, digesting them by lysing (bursting, so to
speak, the organisms cellular membrane)
In this form of immunity, the B cells, a specialized form of WBC,
upon recognizing an antigen, the organism, produces antibodies that
inactivate or kill the organisms.
?Cells which make up the immune system can be found in a typical blood
sample; in addition to red blood cells and platelets, it is the white
blood cells which comprise the immune response (a normal white blood
cell `differential' count is around 5-9000 per cubic millimeter of
blood). Typically, there are the granulocytes which normally make up
60-70% of the white cell total (neutrophils, eosinophils, and
basophils), lymphocytes making up 20-25% (B and T cells), and
monocytes making up the last 3-8% of the total white cell count. These
cells have various duties within the immune response team; however for
the sake of simplicity we can look at our immune cells (white cells)
as having 3 principal functions as `carriers', `secretors', and as
`eaters'. Carrier cells like neutrophils and monocytes have the
responsibility of recognizing an antigen, binding it, and `carrying'
it to other cells within the immune complex. Secretor cells like B-
and T lymphocytes have the job of making and secreting specific
antibodies, as well as a number of cytokines needed to activate and
sustain the immune response. And the eater cells like the monocytes
and T-lymphocytes have the responsibility of detoxifying the antigen
directly as well as mopping up the antigen-antibody complexes made
Illustration of a macrophage and bacteria
Another macrophage, full of bacteria
Illustration of how T-cells and B-cells fight organisms
Activation of a macrophage
This page illustrates how a second exposure generates a larger
response, thanks to memory WBC that produce larger amounts of
This page illustrates an antibody structure, and where the binding
sites for antigen are.
Bacteria, viruses, and fungi that enter our nose and respiratory
system are often eliminated by macrophages, plasma cells, and
antibodies, often without or knowing we?ve been infected. If we are in
good health, and the amount/kind of organisms are small/weak, the
?invaders? are killed off before causing any symptoms. If we are run
down, tired, stressed, or already sick, we are not as able to fight
off any new bugs that come around, taking advantage of our weakened
state. Once the organisms are killed off, they are digested by
macrophages. They don?t actually travel to the intestinal tract.
Organisms that enter the stomach, cause a problem, only if they are
vary large in number. I was once told by a microbiologist that one
needed to consume 10,000,000 bacteria to get food poisoning. Numbers
of bacteria lower than that are destroyed by stomach acid. The dead
bacteria are eliminated from the body, along with digested food. What
is often called ?stomach flu?, common gastritis, is triggered by an
inflammatory response to organisms and bacterial toxins.
Skin rashes you get from systemic infections are caused by the
toxins that many bacteria and viruses produce, or an inflammatory
allergic response to bacterial/viral components. Toxins are cell and
tissue destroying machines, making the notorious organisms anthrax,
the ?flesh eating Step?, and botulism so deadly. The achy feeling of
the flu is caused by chemicals released in the body that raise body
temperature, bringing on a fever, that makes it difficult for most
organisms to survive. In other words, the achy feeling telles you your
body is in defense mode, and a fever is actually a good thing! (To a
degree, pun intended!)
?Many bacterial exotoxins have the capacity to damage the
extracellular matrix or the plasma membrane of eukaryotic cells. The
damage not only may result in the direct lysis of cells but also can
facilitate bacterial spread through tissues. Toxins that mediate this
cellular damage do so by either enzymatic hydrolysis or pore
formation. Bacterial hyaluronidases, collagenases, and phospholipases
have the capacity to degrade cellular membranes or matrices.?
?Rather than a localized wound like the cut skin, what occurs when you
are fighting an infection such as the common cold? What elements of
the inflammatory response are at work? Most of them as in the case of
the skin wound. While there is no need for clotting factors, other
cytokines are indeed at work. For example, histamines are at work
stimulating mucous to be secreted by our air passageways to trap
microbial particles; histamines are also at work causing tearing of
our eyes as an added protection. In addition to the bradykinins which
gives us that `achy' feeling, pyrogens are released which target our
hypothalamus in the brain and `resets' our thermostat allowing our
body temperature to rise (yes, that's how we get that feverish
feeling!). Moreover, other cytokines like the interleukins are busy
activating cells comprising the third level of our body defenses the
?Bacteria have the ability to severly affect their host by the
secretion of toxins. These factors can act on distant sites in the
body and can excert their malicious effect even after killing of the
bacteria. However, some toxins are injected directly into the target
by bacteria attached to the cell surface. These toxins often produce
immediate and severe alterations in eukaryotic cells by interfering
with cellular signal transduction mechanisms.?
?Bacterial toxins control enteral and extraenteral cellular processes.
For example, the heat-labile and heat-stable enterotoxins of
Escherichia coli activate enteral adenylate cyclase and guanylate
cyclase. Verotoxin, which enterohemorrhagic E coli and Shigella
species produce, causes systemic disorders such as seizures and
hemolytic-uremic syndrome (HUS). Other noninvasive bacteria adhere to
the gut wall, causing inflammation. Organisms such as E coli and
Clostridium species are normal enteric flora, pathogenic strains of
which can cause gastroenteritis.?
?Dendritic cells are the key antigen-presenting cells in the lung.?
?Tissue pathology is largely related to the release of toxic
eosinophil products. These products include major basic protein,
eosinophil cationic protein, and eosinophil-derived neurotoxin, which
damage the respiratory epithelium, induce ciliastasis, and influence
mucus production. Tissue injury may also be caused by the release of
reactive oxygen species. The release of platelet-activating factor and
leukotrienes contributes to bronchospasm. In some syndromes, such as
tropical pulmonary eosinophilia (TPE) and CEP, interstitial fibrosis
may result from chronic inflammation. Commonly, lung parenchyma is
affected, but in certain extrinsic and intrinsic syndromes, other
organs may be affected.?
Simply written article on immunity
?Memory Cells by contrast are much smaller than Plasma Cells and don't
immediately secrete anything. Instead, they persist in the body for
many years and may never be activated.
However, in the event that the same foreign Organism returns, they
will develop into Plasma Cells much more rapidly than the original
B-Cells and proceed to secrete their ImmunoGlobulins.?
More on immunity
If any part of my answer is unclear, please request an Answer
Clarification, before rating. This will allow me to assist you
further, if possible.
pulmonary response to antigens
achy feeling + flu + antigen response
Clarification of Answer by
19 Jan 2005 16:26 PST
Hello again audy5000g,
I'm sorry I got carried away on the topic of immunity?I DO love the
topic! It is doubtful you have a simple mind though, as evidenced by
your question! Immunology is very hard to grasp, especially with so
many cells that sometimes are called different things. The human body,
and all living creatures for that matter, fascinates me too! I love to
see how all the systems; cardiac, immune, hormone, urinary,
respiratory, cerebral-spinal, etc. interact.
I have found some simply explained articles for you.
City University of London publishes this well written and illustrated
basic immunology guide:
BreastCancer.org has a good simple explanation:
How Stuff Works has a basic explanation of the immune system here:
Another simple description can be found here:
?The first challenge for the immune system is to know that the skin's
first line of defense has been penetrated. So how does the immune
system know that an invasion has occurred and that invaders have
penetrated the skin? The answer is that certain cells of the immune
system recognize that the proteins of the bacteria are foreign.
Cells of your body have proteins on their surface that the immune
system recognizes and leaves alone. But proteins that are not
recognized stimulate the immune system to make antibodies, which are
proteins that attach to the foreign proteins and make them inactive.
Many antibodies circulate in the blood, while others are anchored in
cells. The free-circulating antibodies can be transferred from one
individual to another by blood transfusions or from mother to newborn
via the milk for the first day or two after birth. The antibodies
attached to cells can only be transferred by transferring the entire
cell, which is makes them less transferable since the recipient's own
immune system would attack the "foreign" cells.?
?How does the body fight invaders?
The immune system has two approaches to attacking invaders:
1. Ingestion by certain migrating cells, such as macrophages and a
type of white cell known as neutrophils.
These cells are like an amoeba. They move around the body and
actually "eat" germs. Once inside the white cell, enzymes break down
and destroy the invader. Cancer cells, which the immune system
recognizes as foreign, are also combated in this way.
2. Binding and inactivation by protective molecules, called antibodies.
These either circulate in blood and lymph vessels or are attached to
membranes of cell surfaces, as described previously. When they bind to
foreign molecules, they make it easier for the invaders to be broken
down. In the case of viruses, the binding can also stop the division
of the virus.?
Follow the ?Next? arrows to follow the sequence.
Here?s an illustration of a white cell ?destroying? a bacteria
The second illustration on this page is an animation of antibody
?An infection from a few bacteria isn't a problem. The bacteria
produce chemicals that eat human cells, but the body can usually fight
them off slowly and wipe out the infections, Timmins said.
"White blood cells basically make a whole oxidative soup to kill
bacteria," Timmins said. "But what wasn't obvious was that they were
also doing something else."
When bacteria reach a critical mass - millions or tens of millions in
population - something changes. They switch from producing the
cell-eating chemicals and start producing a large amount of toxic
chemicals that can kill a person, Timmins said.
"It's kind of like grasshoppers," Timmins said. "You get a few
grasshoppers and they don't do much. They're harmless. But at some
point you get a critical density of grasshoppers and you get a swarm
of locusts that causes immense damage - ruining crops and killing
everything in sight."
It turns out the "something else" that the white blood cells are doing
is releasing chemicals that disrupt the signals between bacteria. They
make a chemical that jams into receptors on the bacteria so they can't
tell each other when that critical mass has been reached, Timmins
"So the body needs to make enough of these oxidants so that the bugs
can never turn on those toxins," Timmins said. "The problem is,
sometimes it can't keep pace. Knowing how this works, though, we can
find new ways to jam their radar, slow the infection down and give the
body a chance to kill off the bugs naturally."
White Blood Cells Fight Infection
Understanding the Immune System
Here is a simple drawing explaining memory cells and antibody. It is
geared to vaccines, but it is the same thing.
Here is an illustration of an allergic reaction, which works closely
like a bacterial infection reaction:
The lymphatic system
Hope this has clarified things for you! Immunology is a very broad and
complex topic, full of puzzles, many of which are yet unsolved. Why
don't you consider taking an anatomy and/or microbiology class at your
local college? You'll be amazed!