Teachable moment in classrooms:

  1. respiratory system chapter – gros anatomy of the respiratory system
  2. lymphatic and immune system chapter – cell-mediated portion of the immune response
  3. lymphatic and immune system chapter – antibody-mediated portion of the immune response
  4. lymphatic and immune system chapter – role of T-helper cells in the immune response

The news item:  Recently, the following news item appeared online:

What to know about the virus with no vaccine, treatment hitting certain states

Currently there is no vaccine to prevent this virus and no specific antiviral therapy to treat HMPV, according to the CDC.

The article states that the new HMPV (human metapneumo virus) is showing up in record numbers in California and in New Jersey. The article also states the symptoms, the treatment options, and mentions bronchitis, pneumonia as most dangerous consequences.

 Why Do I Care??  Respiratory viruses can cause serious illness and death when our bodies cannot resist them. Periodically, reports of new respiratory viruses appear on social media, and the tone of these articles can be quite alarmist. The HMPV is a good example of how we can determine if this new virus represents a lot or a little danger for the general population. Reading deeper into a social media post, or an online article helps a great deal.  Bottom line: don’t just read the headline!!

Plain English, Please!!! First, let’s talk about the properties of the HMPV virus. With every breath we take our respiratory system is exposed to viruses swept along the volume of inhaled air. While we have many layers of defenses against the viruses in the walls of the nasal cavity, pharynx, trachea, bronchi, a few viruses manage to pass through those layers, and penetrate into tissues and into blood, and enter (infect) our cells. For most people the HMPV infection causes only a few days of light cough, nasal congestion, because the natural defenses of the immune system can eliminate the HMPV virus.  There are hundreds of viruses similar to HMPV, and in most people the infection even by totally new viruses is stopped by the immune system.

Second, let’s talk about our natural immune defenses against HMPV. When HMPV infects our cells, two kinds of immune response develop in about 10-14 days. First, the cell-mediated portion reacts to the presence of the invader, and in lymph nodes and other organs millions of fighters, the cytotoxic T-cells are made. These cells are able to travel throughout the body and destroy the HMPV-infected cells. Macrophages and other phagocytic cells digest the debris to remove both leftover viruses and parts of the destroyed cells. Second, the antibody-mediated portion reacts to the presence of the invader, and in lymph nodes millions of plasma cells develop that release large volumes of antibody molecules into the blood. The antibodies spread throughout the body and stick to free-floating viruses and tag them for digestion by macrophages. Those two portions of our immune system are responsible for direct destruction of the virus which results in a quick elimination the HMPV.

Third, let’s talk about why some people can suffer bronchitis and pneumonia despite the natural immune defenses. Because, if our bodies can generate an immune response and eliminate the HMPV invader in 10-14 days, shouldn’t everyone be protected and avoid serious health consequences? Bronchitis and pneumonia are signs that the immune response was not strong enough to eliminate the virus, and bronchioles and alveoli are also infected by HMPV. On one hand, the strength of the immune response depends on the genetic settings that determine the aggressiveness of the cytotoxic T-cells and the speed of antibody formation. On the other hand, the strength of immune response is maximized by the T-helper cells. HMPV infection activated the T-helper cells and then these cells create stimulator molecules called cytokines, to speed up the cell division of cytotoxic T-cells and plasma cells in lymph nodes. Those speedy cell divisions create the large enough number of cells needed for a strong immune response. If only a few T-helper cells are created in response to HMPV infection, or of the T-helper cells make meager amounts of cytokines, then only a small number of cytotoxic T-cells and plasma cells will be created. In turn, the low number of cytotoxic T-cells and plasma cells will bring about only a weak immune response, which will not eliminate HMPV in 14 days, and the virus will spread further, and infect bronchi and alveoli, leading to bronchitis and pneumonia.