Immunity and the Immune Response
It all starts here, with your immune response: the way your body recognizes and defends itself against bacteria, viruses, and any other foreign and potentially harmful substances. You won't stay healthy — or alive — for long if your immune system isn't working properly.
Your immune system is a layered series of defenses, starting with simple physical barriers (like your skin and mucous membranes) and finishing with a sophisticated system of chemical messengers and cellular warriors, designed to fend off attack from all kinds of disease-causing agents.
The immune system works by recognizing antigens and producing specific antibodies to destroy them. An antigen is any substance that is perceived by your body as a threat — and therefore causes your immune system to produce antibodies against it. Antigens can be foreign substances, such as bacteria, viruses, or chemicals, but they also can be formed within your body (examples might be cancer cells or the toxins created by invading bacteria).
The nemesis of any antigen is its antibody. Antibodies are a type of protein custom-made by the immune system to fight specific antigens. Each is unique and defends the body against only one type of antigen.
Many chronic conditions, including diabetes, cancer, and liver disease, can reduce your body's resistance to germs, slow the healing of wounds, and set the stage for infection. So can poor nutrition, certain medications (like steroids), and anything that inhibits circulation and the flow of oxygen in your body, such as hypertension, heart disease, and smoking.
White blood cells, or leukocytes, seek out and destroy invading substances. One type of leukocytes are lymphocytes, which come in two varieties: B cells and T cells. B cells produce antibodies, and T cells attack antigens directly (they also help control the immune response).
Other chemicals include eicosanoids and cytokines, which are released by injured or infected cells and attract leukocytes and other immune cells to the scene to kill off the pathogens.
Your immune system also includes several structures — the lymph nodes, thymus, spleen, and marrow in the long bones in your arms and legs — that produce and store leukocytes.
Everyone has a few kinds of immunity, including:
Innate (or nonspecific) immunity is your first line of defense, a set of built-in barriers that keep harmful substances out of your system. Examples include your skin, your cough reflex, and germfighting fluids like mucus, tears, and stomach acid.
Acquired (or adaptive) immunity, also known as specific immunity, is created as you're exposed to various antigens and your body develops defenses to protect you against them. Your system “learns” to recognize and attack antigens and develops immunity to certain infections.