Introduction

The immune system is a complex network of cells and chemicals. Its mission is to protect us against foreign organisms and substances. The cells in the immune system have the ability to recognize something as either self or invader, and they try to get rid of anything that is invader. Many different kinds of cells, and hundreds of different chemicals, must be coordinated for the immune system to function smoothly.

The immune system can mount a variety of responses to attack specific invader organisms. One of those responses is coordinated by the T-helper cell (also known as the T4 cell), which acts as a kind of orchestra conductor. The T-helper cell tells other cells what to do when this response is triggered. We are interested in this immune response because it is the one that is most disrupted by HIV infection of the T-cells. As HIV succeeds in destroying more and more of these important cells, the ability to fight off some other infections gradually declines. If the "coordinator" of the process, the T-helper cell, is no longer functioning, other blood cells cannot perform their functions, leaving the body open to attack by opportunistic infections.

Normal T-Cell Response To Infection

Let's look first at how the immune response coordinated by the T-cell is supposed to work. Please keep in mind that we will be explaining only one of our body's immune responses.

Any infectious agent that enters your body will eventually be taken up in your lymph system (Figure 1).

This may happen very soon after infection, or it may not happen until the invader has found a niche and begun to replicate. In one of your lymph nodes, the infectious agent (which we will call "Virus" in the figures) will bump into a macrophage (literally "big eater"). The macrophage will ingest the invader (Figure 2).