Medicine: AIDS Research Spurs New Interest in Some Ancient Enemies

The invader is tiny, about one sixteen-thousandth the size of the head of a pin. It consists basically of a double-layered shell or envelope full of proteins, surrounding a bit of ribonucleic acid (RNA), the single-stranded genetic molecule, and often enters the bloodstream of its victim after sexual contact. It is an AIDS virus, and its intrusion does not go unnoticed. Scouts of the body's immune system, large cells called macrophages, sense the presence of the diminutive foreigner and promptly alert the immune system. It begins to mobilize an array of cells that, among other things, produce antibodies to deal with the threat.

Single-mindedly, the AIDS virus ignores many of the blood cells in its path, evades the rapidly advancing defenders and homes in on the master coordinator of the immune system, a helper T cell. On the surface of that cell, it finds a receptor into which one of its envelope proteins fits perfectly, like a key into a lock. Docking with the cell, the virus penetrates the cell membrane and is stripped of its protective shell in the process. Within half an hour, the strand of RNA and an enzyme the virus carries with it are floating in the cytoplasm, the fluid interior of the cell.

Now a remarkable transformation takes place. With the help of the enzyme, the naked AIDS virus converts its RNA into double-stranded deoxyribonucleic acid (DNA), the master molecule of life. The molecule then penetrates the cell nucleus, inserts itself into a chromosome and takes over part of the cellular machinery, directing it to produce more AIDS viruses. Eventually, overcome by its alien product, the cell swells and dies, releasing a flood of new viruses to attack other cells, including more helper T cells and macrophages. The immune system, deprived of a crucial number of those vital T cells, is unable to direct the fight against infection. A host of opportunistic diseases, normally warded off by a healthy immune system, attacks the body. Gradually weakened by the onslaught, the AIDS victim dies, sometimes in months, but almost always within a few years of the first symptoms. By last week this appalling scenario had been played out to its fatal conclusion in some 15,000 Americans. Another 11,500 were under assault, showing the telltale symptoms of the disease, and from 1 million to 2 million others harbored the virus, vulnerable at any time to a final, all-out attack.

Viruses.

The word comes from the Latin for slimy liquid, stench, poison -- and the connotation is appropriate, not only for the AIDS virus but for the untold number of other varieties that have been preying on animals and plants since long before Homo sapiens appeared on earth. Indeed, the current AIDS epidemic is a grim reminder that these infinitesimal, bizarre creatures may be mankind's deadliest enemy. And scientists are warning that a perennial viral threat, the upcoming flu season, could be far more dangerous than usual -- more evidence that these tiny foes are responsible for a large share of human suffering.