Immune System

The immune system is composed of many interdependent cell types that collectively protect the body from bacterial, parasitic, fungal, viral infections and from the growth of tumor cells. Many of these cell types have specialized functions. The cells of the immune system can engulf bacteria, kill parasites or tumor cells, or kill viral-infected cells. Often, these cells depend on the T helper subset for activation signals in the form of secretions formally known as cytokines, lymphokines, or more specifically interleukins. The purpose of this article is to review the organs, cell types and interactions between cells of the immune system as a commentary on their importance and interdependence on the T helper subset. Such an understanding may help comprehend the root of immune deficiencies, and perceive potential avenues that the immune system can be modulated in the case of specific diseases.

There are two types of immune response: innate immunity and adaptive immunity. Both types work together to keep you healthy. The cells of the human immune system originate from stem cells in important key organs in the body: early in life from the liver, and later the bone marrow. The bone marrow continues to produce new cells throughout a person’s lifetime. These organs provide a place for specialized cells of the immune system to mature and develop. From here they go out into the blood stream and to other organs of the body to where they will spring into action when needed.

Innate immunity
Innate immunity is a very quick response to danger signals that are common among microbes (usually bacteria, viruses, and parasites). This is the first line of defense when a microbe enters the body. When you cut yourself, or have food poisoning, your innate immunity responds right away. Some cells, like phagocytic ones, “eat” bacteria and other organisms. Phagocytic cells migrate throughout the body or stay in organs and tissues to wait for invading bacteria or other invading microbes. When they find one, they trap it on their surface, then ingest it (bring it into the cell) and destroy it. Some microbes have developed special outer surfaces that make it hard for the phagocytic cell to trap them. Humans share innate immune components with Drosophila.

Adaptive Immunity
In humans, and vertebrates in general, immune cells are also able to learn and improve immune defenses when they encounter the same microbe several times. This part of the immune system is called the adaptive immune response and this ability is called a “memory response”. Specialized cells work together to recognize a disease-causing microbe and they create targeted responses to the organism. The key to this response is the production of specific antibodies by the cells that are designed to specifically attack the microbe causing the threat. These responses will be “remembered” by the cells so that they can respond quickly the next time this threat is encountered.