With Asthma, Which Came First, Genes or Bacteria?

In my last three posts, I’ve been writing about the puzzling and intriguing association between the microbes in our bodies and asthma.  Research seems to show that the lungs and guts of children with asthma house different and less varied communities of bacteria, fungi, and viruses than non-asthmatic children. 

         Research also seems to show that very early exposure to a great variety of such microbes protects against asthma.  For instance, babies raised in rural areas or born vaginally, are far less likely to have asthma than babies born by caesarian section or raised in “clean,” disinfected urban environments.

         However, these connections are merely associations of one condition with another.  We don’t know if there is a cause and effect relationship.  Perhaps the children with asthma are genetically likely to have the disease, and the same genetic make-up also predisposes them to host specific microbial communities in their bodies.  Perhaps on the other hand, the children without asthma have different genes, that protect them from the disease and, at the same time, allow them to host different and more varied microbial communities.

         This is a special version of the quirky “nature or nurture” problem.  Nature or nurture is a human idea that probably has nothing to do with biological reality.  Many such questions turn out to have complex answers or no true answers at all. Unquestionably, the association of health or asthma with various internal communities of bacteria is complicated.  It is a research adventure full of wonder, worth following for some time to come.



Asthma: Good Bacteria & Bad Bacteria?

In my last two posts (Jan 4 & 7), I’ve been discussing the apparent connection between resident bacteria in our bodies and asthma.

         One of the most interesting findings about this comes from a study by William Cookson and Miriam Moffatt at Imperial College, London.  They found that asthmatics tend to have flu-type bacteria in their lungs, even though they may not be sick.  On the other hand, non-asthmatics’ lungs tend to contain soil bacteria, sea bacteria, and gut bacteria.

         The question is, what is the role of these bacteria?  Do they cause or protect against asthma?  Do they cause or protect against something which itself causes asthma?  Or is the connection something we haven’t thought of yet?

         This is going to be an interesting topic to follow for many years.  There are so many clues and so few answers. 

         I'll have some final thoughts on bacteria, asthma, and human beings in my next post.



Portrait of a Mystery: The Bacteria/Asthma Connection

In my last post, I discussed some of the intriguing association between lung and gut bacteria, and asthma.  The richer and more varied the bacterial community in a child’s respiratory and digestive system, the less likely that child is to suffer from asthma.

         In experiments with mice, one researcher found that many courses of antibiotics seemed to make baby mice more likely to have asthma.  This makes sense, for the antibiotics would diminish the presence of many species of bacteria living inside the mice. 

         This same association between antibiotics and asthma seems to be true of human children.

         But about ten years ago, a study led by Dr Maija Leinonen showed that a possible cause of asthma in humans was infection by the bacterium Chlamydia pneumoniae.  Leinonen thought a protein produced by this bacterium might sensitize patients’ immune systems and make them over-reactive to normally benign substances like dust or pet dander.  She found that a course of antibiotics given to people who had suffered infection by C. pneumoniae alleviated asthma.

         Around the same time, however, Stephen Holgate created a vaccine with dead soil bacteria, and found that this vaccine alleviated asthma symptoms in 67% of the members of a small study.

         These are only two instances of confusing results of asthma studies.  Yet notice that one of the wonders in all this material is the apparent connection between microbes in our bodies and asthma.



Too-Clean Is Making Kids Sick

A childhood disease on the rise is asthma.  Why is this happening?  Clues have been accumulating.  They point, amazingly, to antiseptics, disinfectants, and antibiotics as culprits.

         For nearly two billion years, all life on earth was bacterial.  So when animals evolved, they did so in a bacterial world.  The result is that animals evolved to depend in many ways on bacteria.  All over our outsides and insides are microbial communities.  They consist of thousands of different types of bacteria, along with viruses and molds, and they keep us healthy. 

         Some obvious ways our microbes contribute to our health: They keep away disease-causing microbes by crowding them out, eating them, or poisoning them.  They contribute nutrients to our diets by digesting what we put into our guts but cannot digest ourselves.

         And now we learn that in some mysterious way, our native bacteria may keep us from getting asthma.  Or if we have the wrong microbial communities in our respiratory or digestive systems, we get asthma.

         So far, no one knows exactly how this works.  But statistics show that it’s true: Children raised on farms and in other rural areas are much less likely to get asthma than children raised in antiseptic, Lysol- and bleach-scrubbed urban environments.  Children born vaginally, exposed to bacteria in the birth canal are much less likely to get asthma than children born by caesarian-section.

         Hm-m-m.  What is going on here?  More on this wonder in my next post.



Sorting Out the Different Forms of Life

     During the last third of the 20th century, biologists sorted life into five kingdoms. These were Animalia, Plantae, Fungi, Protista, and Monera. We’re all familiar with animals, plants, and fungi, but what are protista and monera? Protista are all the one-celled creatures whose cells contain a nucleus, and Monera are all the one-celled creatures whose cells do not contain a nucleus.
      One problem with this system of categorizing living things is that it is a human system, based more on what humans see than on what is actually true about the living organisms. For instance, four of the kingdoms, animals, plants, fungi, and protists, consist of creatures made of eukaryotic cells, that is, cells with a nucleus. Yet these are grouped as if they were as different from one another as all of them are from the monerans.
      For a long time, the members of monera were thought to be “bacteria and blue-green algae.” Eventually, researchers realized that those “blue-green algae” were actually photosynthetic bacteria. So actually, Kingdom Monera should simply have been called “Kingdom Bacteria.” But then, in the late 1970’s, a biologist named Carl Woese announced a startling discovery. He had compared RNA from a number of different living types and had found that Monera actually contained two quite different forms of life.
      Woese called the two forms of monerans “eubacteria” and “archaebacteria.” Furthermore, Woese could show that the eukaryiotic forms of life were more closely related to the archebacteria than to the eubacteria. Woese proposed that above the “Kingdom” category in the hierarchy of life forms, there should be a “Domain” category. The Domains would be Eubacteria, Archebacteria, and Eukarya, with Archebacteria and Eukarya closer together than to Eubacteria.
     For quite a long time, the rest of the biological community disbelieved and actively ostracized Woese. But now his domains are accepted and taught as a regular part of biology courses. The names of the Domains have been shortened to Bacteria, Archaea, and Eukarya. Further research has turned up intriguing similarities between eukarya and bacteria, and between eukarya and archaea. Obviously, clues about the evolution of eukaryotic cells provide plenty of work for evolutionary biologists!

Woese, Carl R. and Fox, George E. PNAS, 11/1/77, vol. 74, #11, pp. 5088-90.