In 1987 a doctor sent me tissue from a man he was treating. The man had large swellings under his jaw and was known to be HIV positive. The question I needed to answer: Was the swelling caused by HIV or by something else?
The swellings were from salivary glands called the parotids. I used a technique from molecular biology called in situ hybridization to look for the RNA of HIV. I found lots of it, more than I had ever seen before (Fig. 1), but more surprisingly the HIV was not in the glands but in the lymph nodes (Fig. 2) surrounding the glands. Moreover, the only parts of the lymph nodes that contained the virus were the germinal centers, a part of the lymph node that is essential to a healthy immune system.
Figure 1 A section of parotid gland from an HIV-infected person with large amounts of virus in the germinal centers of the lymph nodes surrounding the gland. In this computer augmented image, areas with large amounts of HIV are green or blue. 4x.
Figure 2 Diagram of a human lymph node showing the major functional areas. The germinal centers are shown in rudimentary detail; they are actually complex centers of activity in the immune system.
