Living with Germs: In Sickness and in Health

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Writing in the journal mBio , researchers from the University of Michigan Medical School and VA Ann Arbor Healthcare System offer microbiome-based evidence that most of the bacteria in the lungs of healthy people got there by way of microaspiration. In other words, they ride in on tiny droplets of saliva that made it from the microbe-filled mouth to the lungs. That means they avoided the movable tissue barrier, called the epiglottis, which keeps most saliva from getting into the lower respiratory tract. By studying the DNA of these bacteria throughout the lungs of healthy volunteers, the researchers confirmed that the population of microbes in the lungs closely resembles the population found in the mouth.

They found that many of the immigrant microbes make their home near the main carina, the spot at the end of the trachea where the airway branches off to the left and right lungs. But some bacteria manage to make it all the way to the deepest reaches of the pulmonary system and reside in the tiny air sacs called alveoli. Wherever the bacteria land, the researchers found, they join a community made up mostly of other recent immigrants.

Few microbes are thought to be long-term residents of healthy lungs. Unlike the gut, healthy lungs are an inhospitable environment for bacteria, with little nutrition and constant surveillance by the immune system.

S11RS03 In Sickness and in Health

Dickson, M. Dickson and his colleagues did their study in eight healthy volunteers who underwent bronchoscopy at the VA. The team obtained the lung bacteria using two techniques to sample nine separate sites in the lungs of each volunteer. One technique, called protected specimen brushing, used a special catheter that keeps bacteria from the mouth and throat from contaminating the samples taken in the airways. Suspicion of such contamination has kept some researchers from fully accepting the results of previous lung microbiome research.

So to test for this contamination, the researchers took one sample on a brush held in the middle of the airway and the rest using brushes that they gently touched to the airway wall. The researchers got other samples through bronchoalveolar lavage, in which they squirt a small amount of fluid into the deepest part of the lung and suction it back into the bronchoscope, bringing microbes along with it.

Taken together, the results suggest bronchoscope-based techniques can be used to study the lung microbiome — in sickness and in health. The researchers emphasize that these volunteers were healthy and had no symptoms that suggested pneumonia or other respiratory disease.

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Dickson notes that microaspiration in healthy people has been observed for nearly a century in studies using medical imaging techniques. Dickson and his colleagues aim to focus future research on what happens in people who have problems with the elimination part of this equation.

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Inability to cough irritants out of the lung, or to carry them out through the sweeping action of hairlike cilia on lung cell surfaces, could lead to more microbes staying longer in the lungs than normal. And that could lead to a higher risk of lung infection.

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  4. As the father of two young children, Dickson also thinks it would be interesting to study how the lung microbiome changes when a person has a viral infection that causes the upper respiratory tract to produce more nasal secretions. He and colleagues have already found evidence that the lungs are filled with gut microbes in critically ill patients.

    How to Stay Healthy When Literally Everyone Around You Is Sick

    This article will serve as the introduction to a multi-part series aimed at understanding the very complex and important topic of how the immune system is able to detect threats, mount appropriate responses, and yet not get out of control. This first article introduces the concept of harmful versus beneficial microbes, how vaccines have impacted health and our understanding of immunology, and the central role of T helper lymphocytes in directing appropriate immune responses.

    We live in a world filled with creatures too small to be seen without a microscope. Most of these microbes are harmless and actually do things that help us. For instance, bacteria in the gut help to break down food into usable parts that we otherwise would not be able to digest. Living with microbes is not only normal but also an important part of being healthy. Cells of the skin, cells lining the airways, and cells making up the walls of the intestines create protective barriers to keep microbes outside of our bodies.

    However, if the microbes get through these barriers, they can flourish and grow, and even harmless microbes can cause dangerous infections. That is why it is important to wash cuts and keep them clean until they heal. There are a few types of microbes that have developed ways of getting through the barriers in humans, even when there are no cuts.

    The fact that cuts are part of normal life and that there are some microbes that can enter the body even when there are no cuts make it necessary for us to defend our bodies. This defense against microbes is the very important job of the immune system. At its most basic level, the immune system is a communication network that consists of signals and detectors to receive those signals.

    Surfaces of cells of the immune system are covered with receptors that help to detect signals from the environment around them. At any given moment, thousands of pieces of information are being received by a single immune cell. The interpretation of these signals is very critical to how the cell responds. Like the signals your brain receives from sensing the world around you through sight, touch, hearing, or smell, immune cells are sensing their surroundings all the time, and hopefully acting accordingly.

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    Since harmful situations are not common, most of the time the immune system does not need to get activated. Scientists who study the immune system used to think that there was not much signaling going on during these quiet times, but now they understand that there is communication occurring even when there is no danger. However, we know a lot more about the signals that the immune system uses to get activated when there is danger, because it is much easier to measure those signals.

    These activation signals can come from microbes, other cells of the immune system, or even cells that are not part of the immune system.

    Can you be too clean?

    When a dangerous microbe does enter the body, there are specialized cells called antigen-presenting cells APCs whose job it is to detect them and capture them see Figure 1. Because there are so many different types of microbes and cells present in the body, there are multitudes of signals and a large number of receptors for them. The study of the cells of the immune system and how they communicate is called immunology.

    While most of what we know about the immune system has been learned in the last 50 years, the field of immunology has roots back several centuries when a method called vaccination was first described. Before vaccines, there were some very deadly microbes that were extremely common in the human population.

    Living with Germs: In sickness and in health - John Playfair - Google книги

    One of the deadliest of these was a virus called smallpox, named for the small sores that infected people got on their skin. Whole villages of people could be killed in a short time by the smallpox virus, and in many ways, smallpox shaped much of human history. That began to change in the late s when some very important observations were made by doctors in the English countryside [ 1 ]. One thing that they observed was that people who had a minor infection with smallpox and survived seemed to be protected from it afterward. Then, doctors noticed that milkmaids and other people exposed to cows were much less likely to get smallpox than everyone else in town. The boy was later protected from getting smallpox. Many more similar experiments became the basis of what we now call vaccination. By , the worldwide effort to vaccinate people to prevent smallpox was so successful that there have been no reported cases of smallpox anywhere in the world since.

    Vaccines have now been developed to protect people from other infectious viruses and bacteria. Microbes like polio, diphtheria, and measles, which used to cause very severe illnesses or death, are much less common today because of vaccinations. It took a long time to actually understand why exposing people to cowpox worked to protect people from smallpox. It turned out that the virus that causes cowpox is in the same family of viruses as smallpox.

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    Although it is not common for exposure to one virus to protect people from a different virus, in the case of cowpox and smallpox the viruses were similar enough that the immune response to cowpox was also protective against smallpox. In the case of most other vaccines, it is necessary to either use a killed version of the actual microbe being targeted, or a non-infectious piece of that microbe.

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    Currently, there are very active efforts to develop vaccines against recently discovered microbes such as HIV, Ebola virus and Zika virus. There is also work being done to keep up with rapid changes that other viruses like influenza flu virus make to avoid being detected by the immune system. In trying to figure out how cowpox exposure protected people from smallpox, the immune system was discovered. Therefore, Edward Jenner has been credited as being the founder of immunology.

    It took until the last few decades for immunologists to understand how the immune system responds to viruses or any other type of infections. It turns out that there are very unique types of immune responses that get activated when different microbes infect us, and it is important for the immune system to activate the correct response in each situation. For this reason, the immune system has many branches, each of which has sets of cells specialized to deal with a specific type of infection.