HIV-Test, often also called "AIDS-test"
The first test used is an enzyme-linked immunosorbent assay (ELISA). This is a test to see whether the blood of a person contains antibodies against the AIDS-Virus HIV. This test can't detect the virus itself or viral nucleic acid but it can detect the antibodies, special proteins, which the immune-system of the infected person has made to fight the virus. If such antibodies are found, the test is "positive". In this case, the ELISA is repeated to be sure of the results.

If this second ELISA gives a positive result, another more sensitive test, called Western blot is done. If the Western blot is positive, a second blood sample is tested in a Western blot. Only if all of these tests are positive, is a person regarded to be "HIV-positive". False-positive results are extremely rare (about 1 out of every 20 000 tests).

Because the immune-system needs some time to make antibodies in quantities in which they can be detected this test can't work immediately after the infection took place. It takes about 6 to 12 weeks after exposure to the virus to develop enough antibodies to measure. A person having an HIV-test during this period might test negative even if he or she is infected. This is called a false-negative result.

An earlier detection of an HIV-Infection is only possible through the direct measurement of the viral nucleic acid in the patient's blood (see "viral load"). But these tests are much more expensive and not used for routine screening.

How were the modern antiviral drugs developed?
In modern drug research scientists investigate the molecular mechanisms of a disease and try to find the most promising targets for drugs. Basic research can be very important, for example, when scientists searched for the cause of AIDS, which turned out to be a retrovirus later called HIV, it was very helpful that they already knew a lot about retroviruses and their characteristics in general.

After the identification of the HI virus, scientists learned about it in detail, its components and the specific roles these components have during the life cycle of the virus in a human cell. For both the identification of the virus and the investigation of its molecular structure and function, many standard procedures of modern biotechnology and gene technology were used. The virus was studied directly by electron microscopy Its genome was sequenced, and all its proteins were characterised and their functions identified. All this data collected by scientists around the world led to our understanding of HIV and the mechanisms of its life cycle in a human cell.

Theoretically, there are many steps in the viral life cycle, which are possible targets for antiviral drugs. So far the best targets are two viral enzymes, the "reverse transcriptase" (RT) and the "protease". The first drug, developed in 1986, was AZT, a so-called RT inhibitor. The first protease inhibitor (PI) came on the market in 1996. PIs are very effective drugs but they can also have serious side effects. All anti-HIV drugs in use today inhibit these two viral enzymes in various ways. Attempts to block other viral enzymes or important structures, e.g. receptor molecules which the virus needs to identify its target cells, are subject to intense research.

Viral load measurement
Viral load measurement means the direct determination of the amount of HI viruses in the patient's blood . What is measured is the quantity of copies of HIV-RNA per ml blood plasma. The methods used are either based on the direct amplification of the nucleic acid (i.e. strong, exactly defined multiplication of the RNA copies in the sample), mainly by PCR, or on the high amplification of the measured signal (branched DNA assay, bDNA). Currently, the lower detection limit is 5 to 20 virus copies per ml plasma, depending on which method is used. These are quite low numbers; in comparison, more than 30 000 viral copies per ml plasma would be regarded as a high viral load. The upper detection limit is about 10 million copies per ml blood plasma.

The viral load is a very reliable marker for the progress of the infection. Today it is the most important indicator for the effectiveness of antiretroviral therapy or for the need to change a current therapy. The aim of the therapy is the lowest viral load possible - at best an "undetectable" level of virus copies in the patient's blood.

T-cell count or CD4-cell count
T4 cells or CD4 cells are a special type of white blood cells, which play an important and central role in the immune system of the human body. Unfortunately, they are also the favorite host cells of HI viruses, which attack and destroy them. A healthy individual has about 800 to 1500 CD4 cells per ml plasma. If there are less than 200 CD4 cells per microliter blood, the immune defense becomes incomplete.

Combined with the viral load the CD4-cell count is a reliable indicator for the patient's condition. The CD4 cells are counted directly from the blood sample using a method called "laser flow cytometry". Through the binding of monoclonal antibodies, which recognize specific surface structures on these cells, the CD4 cells are labelled with special fluorescent markers. This allows scientists to distinguish these cells from all others in the sample and to count them while they are passing a detector.

Washing sperm
The semen of an HIV-positive man might contain high numbers of viruses, even under antiretroviral therapy. Luckily, the viruses do not normally stick to the live sperm cells (which are needed for impregnation). Instead, they are mainly found free in the fluid or connected to dead sperm cells and other cells in the semen. Therefore, it is possible to separate live sperm cells from the free viruses and infected cells. Scientists do this through a kind of 'washing' which includes three steps of careful density gradient centrifugation.

The 'washed' sperm sample is then carefully checked for virus nucleic acid using highly sensitive detection methods like PCR. During this procedure, the remaining sperm cells are stored by cryoconservation to keep them alive. Once it has been proved that the sperm cells are virus-free (i.e. not even the slightest trace of virus-DNA or -RNA has been found) this sperm is used for artificail insemination or IVF.

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