Monera and The Immune System
According to different sources, a disease is any circumstance in which the cells are being attached causing a breakdown in physical or functional health and equilibrium. Therefore, the cold is a disease but being poisoned by the venom of a snake is not.
Most diseases are caused by viruses or bacteria. You'll recall that these two things belong to the kingdom Monera and are very, very old indeed. Bacteria are prokaryotes (no nucleus) whose major benefits are decomposition of dead things, helping you to digest, and extraction of vitamins that, without them, you couldn't do. They also make you sick. Luckily, only about 5% of so of ALL bacteria in the world cause illness and a smaller percentage may cause death.
Bacteria are very basic cells consisting of a cell membrane, cytoplasm, DNA/RNA, and ribosomes. They are also surrounded by a cell wall- which gives them shape. Cell walls are also found in Plants (duh!) and Fungi- but that's another story.
Bacteria reproduce through something called Binary (two) Fission (to split). We just call it Mitosis!
Viruses on the other hand are even simpiler prokaryotes- they have a protein coat, cytoplasm, and DNA/RNA. Notice they have NO ribosomes. Therefore, they cannot reproduce- on their own! They need to hijack a living cell and make the cell reproduce for them. Because of this- and some other stuff- a lot of scientists don't consider viruses to be living. However, there is an equal amount that say they are- sort of like seeds- because, eventually, they do have all 8 life characteristics- even if they steal them from a living cell.
So viruses reproduce through the Lytic Cycle. This cycle is as follows:
1. Infection: A virus has to get into your body
2. Attachment: A virus has to attached itself to a living cell of its chemical choosing
3. Insertion: A virus then inserts its own DNA/RNA into a cell's cytoplasm.
4. Production: The cell's ribosomes read the viral DNA/RNA and produce the proteins needed to make more viruses.
5. Assembly: New viruses are assembled within the cell over and over again- bloating the cell and filling it with viruses.
6. Explosion: The cell explodes or ruptures; releasing many more viruses into the body.
7. Reinfection: Those viruses go on to infect other cells and the cycle begins all over.
Without something to stop it, the viral infection will continue to destroy cells (and systems) until the host dies. Luckily, there is an Immune System: a body system designed to fight off infection and "remember it" for next time. The immune system works like this:
1. A foreign body (pathogen) enters the organism (bacteria, virus, pollen, peanut, glutin, etc.) It just has to have a different chemical signature than the rest of the body.
*2. You've seen this before, you have antibodies for it, your Immune System destroys it before you can get sick.
2. Your immune system hasn't seen it before and allows it to circulate in your body.
3. A white blood cell (WBC) or macrophage detects it as something foreign and attacks it. Antigens (bits and pieces of the pathogen) are left on the outside of the cell.
4A. The antigens trigger Helper T-Cells which multiply and trigger Killer T-Cells which go out and destroy infected cells of the body.
4B. The antigens trigger Helper T-Cells which multiply and trigger B-Cells which begin to make antibodes specific to the pathogen.
5. The pathogen and infected cells are tagged with the antibodies.
6. Killer T-cells, WBC, and spikey proteins seek out and destroy the disease (pathogens and infected cells) by using the antibody tags to find them.
7. The macrophage cleans up any left over pathogens and the antibodies are "stored" in your blood and Lymph system for future use- if needed.
8. You are healthy again!
*IF you have been exposed to the disease before or have been vaccinated against the disease, the purple #2 will happen.
As you can see, it is the WBC that starts the immune system's response. AIDS is not deadly in and of itself. In fact, it's a pretty weak virus. However, AIDS attacks the WBC (lytic cycle) and thus the immune response is weak- if at all. Generally, people don't die of AIDS, they dies of the diseases they can't fight off! A healthy immune system depends on good nutrition and age- the very young and the elderly have weak immune systems (its not built up yet and its worn out).