DEFENDING THE BODY FROM WITHIN

Vaccines, Drugs, and Drug Resistance

Over the centuries, people have tried to supplement the natural immune system with anti-infective agents or to stimulate it with vaccines. A vaccine is a preparation of all or part of an infectious agent that primes the immune system to recognize the agent but does not produce the disease. Vaccination, the process of administering a vaccine either by injection or by mouth, developed from observations that people who recover from some diseases become immune to those diseases. Vaccination may have been practiced in China as early as the 6th century. Anti-infective agents, possibly derived from mold as well as other natural sources, have also been used for centuries. It is not clear how effective they were, however.

The 20th century saw the sustained use of natural antibiotics such as penicillin and of synthesized antimicrobial drugs. The popularity of these "wonder drugs" combined with the ability of some pathogens to survive drug treatment has led to the development of resistant organisms. Resistance develops when a drug fails to kill organisms protected by a particular genetic background, which then go on to grow and multiply. Pathogens may develop resistance by acquiring genes from other organisms, through recombination, or by the occurrence of mutations.

© T. Larsen, The Scripps Research Institute

The unique talents of viruses. Viruses are difficult to defeat because of their strategy of gaining access to cells and taking over their protein synthesis functions. This model of HIV shows the surface glycoproteins that have evolved to fit specific T cell receptors and allow HIV to enter the cell. Once inside, the virus puts the cell's own machinery to work producing more HIV.

Parasitic gangs — team strategies used by malaria
Recent research shows that different strains of malaria can combine forces to defeat the immune system. A strain of malaria that would be defeated, if alone, can escape detection when a similar but not identical strain is also present. When spotted by the immune system, antigen fragments from one parasite block detection of antigen fragments from the second strain, allowing this other strain to slip through unnoticed and cause disease.

The ways of Helicobacter pylori:
a new look at antibiotics?
H. pylori, a bacterium associated with stomach ulcers, itself produces an antibacterial peptide. These antibacterial agents do not harm H. pylori but do inhibit other bacteria that might otherwise invade its territory. As shown here, researchers separated H. pylori proteins based on their differing solubilities and were able to identify those peptides that had an antibacterial effect. Now they are working on developing these substances as therapeutics.

Graph showing differential solubility and antibacterial activity.

Gastroscope.
Used to detect stomach ulcers through visual internal inspection and to snip samples of stomach tissue for later laboratory examination.