This blog has been created partly as a companion to Chemistry for the Biosciences, the textbook that I co-author with Tony Bradshaw, and to act as an archive of posts I write for other sites (particularly the OUPblog). Like the book itself, it explores how life on the scale of atoms and molecules has an impact on biology - at the scale of cells, tissues, and organisms - and seeks to demystify a range of biological and chemical concepts.

The blog's name takes as its inspiration the cover of the first edition of Chemistry for the Biosciences, which depicts a gecko seemingly clinging to its surface. To find out what links geckos to chemistry, read this.

Saturday, 29 January 2011

The healthy side of germs

Here is the article that secured me a runner-up spot in the 2001 Daily Telegraph/BASF Young Science Writer competition. It doesn't have much to do with the other posts on this blog, but I thought it worth giving it an airing.(Note that this was written in 2001, so some of the science may haved moved on in the intervening years.)

“Go and wash your hands.”

“Don’t play with that – it’s filthy!”

As children, we’re left in no doubt that getting into the habit of keeping clean is a good thing. But there is growing evidence that being too clean can actually harm our health. When it comes to staying healthy, germs may be able to teach us a thing or two.

From birth our immune system calls on an army of specialist cells to destroy potentially dangerous intruders, such as bacteria and viruses, before they destroy us. But invasion by bacteria is not always a bad thing. As Professor Graham Rook, of the Royal Free and University College Medical School points out, we have 1.5 kilos of quite harmless bacteria in our gut alone. And bacterial infection may play a vital role in educating the immune system to grow in a balanced and more effective way.

Recent years have seen a huge rise in allergy-related illnesses such as asthma. Asthma can be triggered by allergens in the air, such as pollen and air pollution. But these allergens don’t cause the disease in the first place. Indeed, studies have shown that asthma is less common in Leipzig, East Germany, which is highly polluted, than in Munich in the West, which has cleaner air.

Instead it seems that a poorly educated immune system may be to blame.

Our immune system contains various types of white blood cell including T Helper 1 (Th1) and T Helper 2 (Th2) cells. The activity of these two types of cell needs to be balanced for the immune system to work efficiently. If there are too few Th1 cells in circulation then the balance swings towards Th2 cells. One ‘side effect’ of the overabundance of Th2 cells seems to be an increased susceptibility to inflammation. In the case of asthma it is the airways that become inflamed, making breathing difficult.

But how does the balance of Th1 and Th2 cells become upset?

A lack of Th1 cells may arise if they aren’t stimulated to proliferate at high enough levels. And one important stimulus is exposure to bacteria.

However in today’s clean society young children are being exposed to less bacteria than was the case just decades ago. Gone are the days of grubby faced children being called in to tea after spending an afternoon ‘mucking around’ the garden. Today, Playstations have replaced playing in the dirt.

“We need an input of certain bacteria to set up correctly the regulation of the immune system,” says Professor Rook.

But by living in a clean and hygienic environment it seems that we’re denying ourselves exposure to these important bacteria. And without this input from bacteria our immune system isn’t being ‘educated’ to operate as it should.

So how do we overcome this problem? According to Professor Rook, whose research looks at ways of countering the problems of clean living, we needn’t resort to living a life surrounded by dirt.

“We need to identify the necessary things that hygiene deprives us of, and put them back as vaccines or probiotics,” explains Professor Rook.

Essentially this means educating the immune system ourselves. If our Th1 cells aren’t being exposed to the necessary bacteria in the course of nature, we need to take controlled steps to ensure that this vital exposure occurs.

Initial clinical trials in humans are proving positive. Mycobacteria are a family of bacteria whose members include harmless species that are prevalent in the environment, in untreated water and soil. In the laboratory these bacteria can be shown to educate immune cells by changing the way they recognise allergen. In trials led by Dr Ratko Djukanovic at Southampton General Hospital, individuals suffering from allergic asthma have been injected with a vaccine containing dead, heat-killed Mycobacterium vaccae. After a single injection, the vaccine has been shown to partially inhibit allergic reactions that usually occur in the lungs of asthmatics.

“Further clinical trials are needed to investigate the potential of this vaccine as a treatment for asthma,” says Dr Djukanovic, “but our initial results are encouraging.”

So, although we’ve got some way to go until we fully understand precisely what bacterial input is needed to educate our immune system effectively, maybe parents need to be less hesitant about letting their children get ‘close’ to Nature.

Perhaps a bug a day can keep the doctor away...?

Strachan, D.P. (2000). Family size, infection and atopy: the first decade of the “hygiene hypothesis”. Thorax 55(supplement): S2-S10

Hopkin, J.M. (2000). Atopy, asthma and the mycobacteria. Thorax 55: 443-445

Rook, G.A.W., and Stanford, J L. (1998). Give us this day our daily germs. Immunology Today 19: 113-116

Cookson, W.O.C.M., and Moffatt, M.F. (1997). Asthma – an epidemic in the absence of infection? Science 275: 41-42

Farooqi, I.S., and Hopkin, J.M. (1998). Early childhood infection and atopic disorder. Thorax 53: 927-932

Von Mutius, E., Martinez, F.D., Fritsch, C., et al. (1994). Prevalence of asthma and atopy in two areas of West and East Germany. Am J Respiar Crit Care Med 149: 358-364

von Mutius, E., Pearce, N., Beasley, R., Cheng, S., von Ehrenstein, O., Bjorksten, B., and Weiland, S. (2000). International patterns of tuberculosis and the prevalence of symptoms of asthma, rhinitis, and eczema. Thorax 55: 449-453

Camporota, L., Corkhill, A., Long, H., Lordan, J., Stancui, L., Tuckwell, N., Cross, A., Stanford, J.L., Rook, G.A.W., Holgate, S.T., Djukanovic, R. (2001). A randomised, controlled study of the effects of Mycobacterium vaccae (SRL172) on allergen-induced airway responses in atopic asthma. Personal communication from R. Djukanovic, March 2001.

Professor G. A. Rook – personal e-mail correspondence (February 2001)

Professor J. M. Hopkin – personal e-mail correspondence (February 2001)

No comments:

Post a Comment