Our immune system does a remarkable job of defending us against disease-causing microorganisms.
Unfortunately, sometimes it is overrun by too much stress and too many microbes.
Taking key supplemental nutrients can provide a major advantage for the immune system and allow it to effectively fend off larger amounts of stress and microbial debris.
To strengthen the immune system, follow a low-sugar, nutrient-dense diet. This would include loads of non-starchy veggies, herbs, superfoods and healthy fats. Bone broth, medicinal mushrooms and sulfur-rich veggies such as garlic and onions offer powerful support.
Here are some key supplements to strengthen the integrity of the immune system.
1. Omega-3 fatty acids
Omega-3 fatty acids cannot be synthesized in normal human metabolism and thus must be derived through diet. These fats play an important role in the cell membrane and the receptor sites that bind hormones and neurotransmitters.
Supplementing with the long-chain EPA and DHA, the kinds of omega-3 we find in seafood, provides the body with incredible neurological and immunological support. These powerful long-chain omega-3 polyunsaturated fatty acids balance the omega 6:3 ratio and create an anti-inflammatory reaction in the body. This reaction helps calm the immune system and keep it firing with the balance, synchrony and precision necessary for long-term health. 
Clinical studies have shown the omega-3 DHA in particular powerfully boosts your immune system.
2. Gamma-linoleic acid
Gamma-linolenic acid (GLA) is a critical omega-6 fatty acid that can be found in borage oil, evening primrose oil, black current seed oil and hemp. Unlike other omega-6 fatty acids, GLA helps control inflammation throughout the body when incorporated into the membranes of immune cells. 
GLA has proven benefits in inflammatory diseases such as eczema, acne, asthma and rheumatoid arthritis. It is also shown to prevent the formation of atherosclerosis and cancer. 
Beta-glucan is a powerful immune-stimulating compound found in several mushrooms, yeasts and other foods. Beta-glucan is a polysaccharide that is made up of multiple sugar molecules linked together. The major beta-glucan molecule is called beta-1,3-D glucan.
Polysaccharides are a diverse class of macromolecules that have a high capacity for carrying biological information due to their large structural variability. Beta-glucans are known by scientists as “biological response modifiers” that bind to the surface of innate immune cells, which allows the cells to have better coordination in their attack. This reduces the tendency toward auto-immune reactions and hyperinflammatory activity when the body is under attack. 
Our intestinal system and mucosal membranes (sinuses, respiratory tract, genitalia, etc.) are lined with billions of different bacterial colonies (We are a living bacterial hotel). Progenic or probiotic bacteria work in symbiosis with us (help promote life), whereas pathogenic bacteria create toxic waste and promote disease in our body.
Probiotic supplementation has been shown to modulate the immune system and reduce whole-body inflammation.  Supplementing with probiotics has also been shown to improve immune strength and help prevent the common cold and flu as well as other bacterial and viral conditions. 
5. Vitamin D3
Vitamin D deficiency is a current epidemic in our society today affecting 90% of our world’s population. According to vitamin D expert Michael Holick, MD, PhD, “We estimate that vitamin D deficiency is the most common medical condition in the world.”  It is clear that most people are not getting enough healthy sun exposure.
Vitamin D has been shown to suppress most elements of the adaptive (inflammation-mediated) immune system while inducing most elements of the innate immune system.  Thus, D3 prevents and effectively treats autoimmune diseases by suppressing adaptive immunity while enhancing the first line of defense against invading microorganisms by strengthening innate immunity.