Search This Blog

Friday, 28 November 2014

Ebola and the immune system

I’ve often wished the immune system had a different name. One that sounded a lot more grand and complicated. It slips easily off the tongue and gulls people into thinking that it’s no more complicated than their central heating system. And that the equivalent of a tweak of the thermostat (in the form of a pill or a foot massage) can give “it” a quick boost. When researching my book I realised that it’s a system of a very different kind – more like, say, the complexity of a city like London with its workers, businesses, buildings and transport networks.
There are two main divisions to the immune system. The emergency “innate” division kicks in the minute you have a wound. On a much slower timescale the “adaptive” division learns about all the bacteria, viruses and proteins in your environment – which to ignore and which to attack with antibodies the next time they crop up. There are many different types of immune cell (“white blood cells”) and new sub-types are discovered regularly. They produce a vast array of complex proteins called cytokines that also play a role in attacking pathogens. Part of what we mean by “immune system” is this interacting mass of cells and proteins that flow through blood and tissues during health and illness. But there is more. The permanent structures of the immune system are the bone marrow, which is the production unit for replacement immune cells, and the lymphatic system that monitors threats throughout the body.
As in cities, balance is important. You don’t need a rail system that varies its timetable unpredictably. Neither do you need an immune system that is over- or under-active. Everything has to be modulated to keep things running smoothly so as to prevent not only infection but also self-damage. Diseases associated with an over-active immune system include all the auto-immune diseases, allergies and inflammatory conditions. Toxic shock, sepsis and the cytokine storm (which can occur in pandemic flu) are more sudden and much more deadly over-reactions.
Some illnesses are not just attacked by the immune system – they directly infect immune cells and interact with them in complex ways. It’s well known that the HIV retro-virus directly attacks immune cells, using them as a base and slowly undermining their work. TB, caused by a bacterium, also infects immune cells – the ones that normally engulf and destroy bacteria entering the lungs. Ebola too infects immune cells, and progresses far more swiftly than HIV or TB. It does so by using infected immune cells to spread the virus throughout the body. Ebola is also able to damp down aspects of the immune function. But that is not all. The high fever and inflammation of the later stages of the disease are part of a massive immune over-reaction that contributes to death. 
There are various scientific initiatives attempting to tackle this unusual virus but the solutions are not simple.
There are some anti-viral drugs undergoing accelerated trials but it would be surprising if they make a significant impact. The might of the pharmaceutical industry has yet to produce a range of wonder-working anti-virals for other diseases. Anti-retrovirals, used for HIV, are probably the biggest success, despite all their limitations. Vaccine development is a long and difficult road and vaccines in current development are a while away from any prospect of a  mass roll-out. The experimental biological treatment ZMapp is a product of immunological research. It’s a combination of artificially produced antibodies that lock on to specific targets on the Ebola virus, disabling it. It is to be hoped that ZMapp works, and that one day it can be produced in large enough quantities to be useful in bringing outbreaks under control. However production methods are complex involving a lot of careful work by technicians and the growth of cloned cells in laboratory conditions. This process is not at all like the factory production line that produces conventional chemical drugs. My feeling is that science is very unlikely to come up with any quick answers, with mass impact, in the next few months.
In the meantime though, simple nursing measures like infection control and putting up a drip can save lives. As Christmas looms we are asked to contribute to a wide range of charities but this year many of us will perhaps consider that paying for some nursing supplies for Ebola stricken areas is the most urgent call on our generosity.

No comments:

Post a Comment