Since the 1980s Human Immunodeficiency Virus (HIV) infections and Acquired Immunodeficiency Syndrome (AIDS) have become an increasing concern for the healthcare service. The modern Immunology laboratory, in collaboration with other clinical disciplines has an important role to play in management of patients with HIV by quantifying the progress of the disease in terms of the amount of virus present and the number of viable cells of the immune system that remain.
The Human Immunodeficiency virus principally infects specific cells of the human immune system called CD4 Tcells. In healthy individuals these cells are important for organising the appropriate immune response against infection. Left untreated these infected cells are gradually depleted so that the immune system is gradually less able to mount effective responses. When the immune system is severely compromised the patient will develop AIDS when he or she becomes susceptible to serious opportunistic infections, including Tuberculosis and Syphilis. It is therefore important to monitor the degree of infection and state of the immune system so that appropriate drug regimes can be used to delay the onset of AIDS and to treat opportunistic infections.
The immunology laboratory makes use of two very different techniques in the monitoring of HIV infection once it has been initially diagnosed by the presence of HIV specific antibodies. We can measure the actual amount of viral infection within an individual by measuring the “viral load”. This can be done in several different ways that all fall under the general term of “molecular techniques”. One such technique is real time PCR. The second measurement that we can make is directly related to immune competence but also correlates with viral load. This is the quantification of the number of CD4 T cells that the patient has at any one time during HIV infection. This measurement is carried out by a technique called flow cytometry that uses the unique characteristics of white cells in the blood to identify and quantify CD4 T cells.