Medicine: AIDS Research Spurs New Interest in Some Ancient Enemies

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1) The virus can avoid detection by hiding inside a cell's DNA. It also can spread from cell to cell without ever entering the bloodstream; it does so, in part, by causing cells to fuse together. Thus, says Microbiologist Ashley Haase of the University of Minnesota, "even if you have antibodies to the ; virus circulating in the blood, they won't be able to destroy the infection."

2) The AIDS virus is present in very small quantities in the blood, even in the case of a full-blown infection, and thus makes a difficult target. (The small quantities may also help explain why AIDS is not especially contagious and spreads only by intimate contact.)

3) The AIDS virus reproduces and mutates at a much faster rate than most other viruses, frequently changing the structure of its surface antigens, the protein markers on its envelope. By the time the immune system has produced an antibody that recognizes and goes after a particular antigen, the antigen may have changed beyond recognition.

4) As its "ultimate weapon," notes Immunologist Elaine DeFreitas of Philadelphia's Wistar Institute, the virus thrives in helper T cells and macrophages, "the very cells that are sent to destroy it."

Viruses have even been implicated in such autoimmune diseases as insulin- dependent diabetes, rheumatoid arthritis and multiple sclerosis. In these disorders, the immune system appears to be confused and attacks body tissue as well as foreign invaders. How might a virus provoke the immune system to attack its own body? Immunovirologist Robert Fujinami of the University of California, San Diego, may have discovered one way.

Fujinami has been investigating an autoimmune disease called acute postinfectious encephalomyelitis, which occurs as a complication in about one out of 1,000 children who get measles. Like MS, it is a degenerative disease of the myelin sheath, the insulating layer that surrounds nerve fibers in the central nervous system and helps speed the passage of the nerve signals. Strangely enough, the disease strikes some ten to 14 days after the measles virus has completely disappeared. Fujinami has found that portions of the protein component of the measles virus, in what is called "molecular mimicry," closely resemble myelin's basic protein. Thus, he suggests, "if one makes an immune response against the virus, then conceivably the same response could attack the central nervous system."

Some scientists believe that still undiscovered "slow viruses" are responsible for neurological disorders like kuru and Creutzfeldt-Jakob disease -- which may develop decades after the victim is infected -- and perhaps for Alzheimer's disease too. But because such viruses have never been isolated and because of the nature of these diseases, some researchers suspect that a mysterious, entirely different infectious agent is involved.

Viruses are not all bad news. Despite the woes that they have brought, they probably have contributed more to humanity than just exotic varieties of Dutch tulips. Some scientists think the ubiquitous creatures may have an important and perhaps even beneficial impact on evolution. They suggest that by rearranging the DNA in chromosomes, and by transferring genes from one species to another, viruses can impart characteristics to a plant or animal that help it to not only survive but dominate and edge out competitors.