The human body has a pretty good immune system. Because it’s so crucial to our health, scientists and doctors have been studying the immune system intensely for a long time. A good deal is known about it, even down to the molecular level. This study of the immune system, besides being good for a general understanding of how our body fights off disease, has often been the gateway for the discovery of new drugs and treatments. Given all the work that’s been done, you’d think there would be few surprises.

Here’s a recent and important surprise: Researchers at the University of Cambridge School of Clinical Medicine (U.K.) were tracking the antibodies that attach to invading viruses. It’s long been thought (assumed, really) that once the virus manages to penetrate a cell, any antibodies attached to it are lost. It turns out they’re not.

They discovered that at least some of the antibodies attached to an invading virus remain. Once inside the cell, in the material called the cytosol (the main fluid content of cells), the antibodies attract a very specific protein molecule, identified as TRIM21 (tripartite motif-containing 21). This protein happens to have more affinity for antibodies than any other receptor. In the biologists’ lingo it recruits (more like Shanghais) the virus+antibody combination and starts it on a chemical pathway to molecular degradation. In the colloquial, the virus falls apart and is removed by the cell’s disposal system.

This ‘last line of immunity’ defense is generally effective, though obviously not always. The researchers also discovered that increasing the amount of TRIM21 in the cytosol increased the effectiveness. While they haven’t yet established the all the why’s and wherefore’s, it seems that working with TRIM21 specifically – and in general much more research on the ability to attack viruses while within the cell – could be a new avenue for treatment of viral infections.

Don’t jump to the conclusion that this surprise discovery presages a cure for major viral diseases (“… a cure for the common cold!”). It might, but that’s a long way off, if ever. Nevertheless, this is an important new piece of knowledge – by analogy, the discovery of a new battleground against viral disease. Now it’s up to further research to see what can be done with it.

The details of the study are published online, November 2, 2010 in the Proceedings of the National Academy of Sciences (PNAS), Antibodies mediate intracellular immunity through tripartite motif-containing 21.