When you think of your immune response do you consider how to support immunity by maintaining the health of your gut? Likely not - but remember your gut contains more immune tissue then any other single site in the body, and is a first line of defence, because it is an actual interface with the outside world. 
Consider that even though it has numerous sphincters and points of closure, your gut is basically a semi-permeable tube that runs through your body-proper. Being that it is constantly exposed to foreign substances from the outside world in the form of what we ingest, it makes perfect sense that there is so much immune surveillance located there...and that it is an extremely common place for inflammation (think "fire") to start.
We've all heard the phrase "It's the Dose that makes the poison." Well, when it comes to infection with viruses, bacteria, fungus etc., I would say "It's the HOST that makes the poison." Meaning with so many different kinds of possible infections, different peoples' reactions to them can vary from death on one extreme, to mild or non-existent on the other. Of course, the virulence/pathogenicity of bugs varies, but take the same bug - different person, and you can get a dramatically different response. If it is a nasty bug in question, preventing or calming the inflammatory "cytokine storm" that may accompany it...and can become runaway, is key to a good outcome. 
So the obvious question then becomes: to prevent excess, pre-existing inflammation in the body what are the parameters we need to be concerned with? I submit that one of the most important parameters that determines whether or not you will have a balanced, effective immune response when dealing with an infection...or not, is our how reactive/non-reactive our gut is to begin with.
Consider that if the "fire" in your system is already "stoked and blazing", when you add an infection on top of it the more likely it is to get out of control and "burn your house down". It makes perfect sense then that one of the best measures we can take to prevent the fires from starting is to take steps where inflammation is most likely to be initiated, i.e. where the most immune tissue is...the gut!
Immune Response And Inflammation
Without even considering infection, if noxious substances come "down the pipe" in your gut, the inflammatory immune responses that follow can be extremely degrading for your health and well being, as those people with food allergies or celiac disease can attest. Yet, if undesirable/pathogenic bacteria have actually set-up shop in your intestines... a condition known as dysbiosis... the resulting immune-response creates inflammation that can be ongoing, and contribute to a wide array of other health conditions.  This includes immune dysfunction, and being predisposed to worsened outcomes from a viral infection.          
So if your gut is a MAJOR potential source of inflammation...(% -wise it is actually the MOST likely source of an inflammatory immune response)... and pre-existing inflammation predicts a worse outcome from an infection, or any other inflammatory challenge, (the list of which are practically endless), how do you go about balancing out gut-mediated immune responses, and increasing their "efficiency"?
[Note: By "immune efficiency" what I mean is to have an effective immune response that doesn't create a lot of unnecessary inflammation in the process. I have discussed this concept before in this article - Why Viruses Make You Feel "Sick" And What You Can Do About It
When it comes to the gut the answer is to take advantage of the symbiotic relationship between us, and the "friendly" bacteria, i.e. Probiotics.
Why Probiotics Are Important For Healthy Immunity
You see when good bacteria predominate in our gut they break down dietary fibres to produce what are called Short Chain Fatty Acids (SCFAs).  In turn these SCFAs nourish the cells of our intestines, provoking them to produce a healthy, desirable coating of mucus, which creates a protective barrier between the immune tissue of our gut and noxious foods, pathogenic bacteria, viruses, etc.    So not only do the SCFA' make the gut lining happy, but the protective mucus barrier they elicit moderates the immune response, preventing it from being exaggerated, or run-away, thereby exerting an anti-inflammatory influence.   
Hence, it is logical to do some "immune care-taking" in your gut by ensuring your intake of a wide range of dietary fibres, along with probiotics.
Yet, the response to this is often "Sure...but which Probiotic should I use?"
Which Probiotics To Use? Our Experience With DDS® -1 Probiotics
At Optimum Health we have had the privilege of observing which products perform well in different situations since 1993. Even back then I was using DDS®-1 combined with Bifidobacterium because I found that both personally and in my clients it produced by far the most marked calming of allergic and other inflammatory immune responses. These observed responses included calming histaminic reactions, improving digestion and intestinal discomfort, and calming sites of systemic inflammation as well...overall making a person feel better more consistently than any of the other hundreds of probiotic formulations that I or my clients, or our customers, have used.
DDS®-1 and its associated strains of bifidobacterium, and others have decades of research behind them dealing with gut health and immunity.
Check out the links below:
https://uaslabs.com/research/dds-1/ ... The DDS®-1 difference
https://uaslabs.com/research/uabla-12/ ... UABla-12 bifidobacterium
Also see this former article - What Do Probiotics Do For Allergies?
In 2016 Optimum Health Vitamins had the fortunate opportunity to add the DDS®-1 / Bifidobacterium combination to its line of products, and jumped at the opportunity. Not surprising, given that we had been using and recommending it as our number one probiotic for over 20 years already, because it produces RESULTS!
Also, remember that what is more important than a high number of probiotics per capsule, say 100 Billion, is the TYPE of probiotic, and its characteristics....essentially its strength. Adding 100 Billion bacteria to the tens of Trillions already in your gut is like adding a pinch of sand to a five-gallon pail of sand. What matters is how active it is once it gets there.
Yet, also remember that we are all individual. What works for one doesn't always work for another. The make-up of the bacterial populations in our gut is as unique as our fingerprint. With multiple trillions of bacteria in an average gut, this is to be expected. When it comes to which is right for you, even though we have seen the best results with DDS-1, it may involve some experimentation. But I would recommend not settling for a product where you don't notice anything. When people find the right probiotic formulation for their body's makeup the improvement in gut health, digestion and how you feel can be unmistakable. Improving your immunity in these times is definitely a huge bonus!
Until next time,
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257638/ Gut microbiota and inflammation
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3294426/ Into theEye of the Cytokine Storm
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5224679/ Agents to reduce cytokine storm
 https://www.sciencedaily.com/releases/2020/05/200521165706.htm Preventing 'cytokine storm' may ease severe...
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4056765/ Role of the Microbiota in Immunity and Inflammation
 https://www.frontiersin.org/articles/10.3389/fmicb.2018.01835/full The Human Gut Microbiome - A Potential Controller of Wellness and Disease
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7187844/ J. Clin Virology 2020 Predictive factors for disease progression in hospitalized patients with coronavirus disease 2019 in Wuhan China
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7189186/ SARS-CoV-2 infection and obesity: Common inflammatory and metabolic aspects Diabetes Metab Syndr. 2020 July-August; 14(4): 469–471. Published online 2020 Apr 29
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1773837/ SCFAs stimulate mucin production
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991899/ trillions of bacteria in our gut