1. Viral Infections and Immunity
As living creatures, nature has equipped us with a biological defense system that has evolved to protect us from threats in our environment. This system is called the immune system, a physiological mechanism to protect our body, along with the five senses including vision and hearing. The naturally inherited component of the immune system is called the “innate immune system.” Its responses comprise a relatively moderate biological defense. The blood cells of the innate immune system accumulate experience recognizing invaders and gradually develop to establish “acquired immunity.” This acquired immunity will continue to develop and become capable of fighting against specifically targeted invaders. But on the other hand, it can be the cause of problems such as allergic reactions, which are patho-physiological phenomena. These allergic reactions are triggered as part of biological self-defense reactions to protect our body. The nature of the immune system is to distinguish, and to try to eliminate, every “non-self” molecule. This is an amazingly well-organized system that has enabled animals on earth to enjoy their lives in Paradise full of vitality. In peaceful daily life, an immune over-reaction of inflammation (a pathological immune response) may occur merely due to insect bites or abrasions. When this response expands to the whole body, it may trigger a fever, which is also a type of inflammatory reaction.

2. Infected with a Virus but Asymptomatic?
Viruses are broadly classified into DNA or RNA types. Viruses are parasites in cells and have not been categorized either as organisms or as inanimate objects since their discovery, but cells, which belong to organisms, are considered to be living. A virus enters the cell of a living host, establishes itself, and then reproduces. A virus can parasitize only specific cells of certain animals. These types of cells are found to have antenna-like structures on their surface. This phenomenon is called “species-specificity.” As an example, a virus that parasitizes and infects only the cells of a bat may invade the respiratory or lung cells (organ specificity), reproduce itself, and then destroy cells. This incidence is followed by release of an inflammatory substance called arachidonic acid, which will be described below, and triggers pneumonia in the bat. Part of the RNA in this virus coexisting with bats may sometimes mutate. This phenomenon can enable the virus to penetrate the human respiratory tract and lung cells. The most important strategies to fight against these types of viruses are vaccine creation, clinical protocols, and the development of pharmaceutical products that can interfere with RNA replication of the virus.

When infected with a virus, some patients are asymptomatic and show no inflammatory response, while others develop symptoms and inflammatory responses. What causes such great disparities? It is necessary here to understand the basic biological reactions of the body, which consists of “immune reactions” and “inflammatory reactions.” Inflammation is initiated with the release of arachidonic acid, an important fatty acid. This substance is found in every cell membrane in our body. Its release signifies that inflammation is initiated by cell destruction. Arachidonic acid triggers a cascade of reactions of various cytokines (bioactive substances), followed by development of visible reddening and painful inflammation. Inflammation is an excellent, but excessive biological defense reaction that occurs in living bodies. This excessive inflammation can actually destroy the living body. This phenomenon is called a “cytokine storm.” It can sometimes lead to death.

3. Viral Infection and Innate Immunity
Now, I would like to bring the topic back to immunity. Although our body is equipped with the immune system, which plays defensive roles against various foreign invaders, this system doesn’t work well against a foreign entity on its first encounter. The immune system may not be able to apply an appropriate strategy against the invader, or may even fail to defend against the virus. Human beings don’t have defense measures strong enough to fight against viruses (antigenic substances) that they have never encountered. Therefore, it is extremely important in these cases for the immune system encountering new, unknown invaders to enhance the potency of the innate immune system. The number and ability of natural killer (NK) cells, which belong to the innate immune system, are probably the major force capable of attacking virus-infected cells. The mechanism of activation and proliferation of NK cells has been studied all over the world, and numerous findings have been reported. If we can enhance the ability of the innate immune system, while maintaining harmony in the overall activity of the immune system so that it can function in a well-balanced condition, we believe that this is the most practical approach to take as we await development of antiviral agents and vaccines.

4. What Can Be Done Against Viral Infections?
Finally, we would like to consider what we can do to protect ourselves from contact with viruses or aerosol transmission? Maintain a distance from other people and avoid having conversations in close proximity. Wash your hands carefully with soap and disinfect your fingers with a hand sanitizer. Gargling works well to block viral transmissions that target respiratory tract cells. When you wash the mouth and throat by gargling, you should use isodin or mouthwash, and swallow it to the last drop. Smoking paralyzes the bronchial epithelial cells, which results in deterioration of their ability to eliminate foreign matter. Smoking must be stopped. Although the fiber mesh of a mask is not thick enough to block virus particles, it can be used to keep our throat moisturized, to protect ourselves from the microdroplets of others, and to avoid spewing our own droplets to others. The major components of the immune system are blood cells and cytokines, which are both types of protein. Our diet plays a key role in the renewal of blood cell populations and cytokines. A well-balanced diet is indispensable to the immune system. A desirable example is the traditional Japanese diet with the main dish of fish. We should eat at least five eggs per week, since eggs are essential for cell membrane formation. Leafy vegetables are required for DNA replication. Eat a wide variety of side-dishes, and refrain from taking too much of any one food. If you try to maintain and boost the immune system with a healthy diet, it will help you not only to prevent viral infection, but also to prevent various lifestyle-related diseases.