A certain group of salivary glands named the submandibular glands lies in wait kind of behind the sublingual glands under the tongue(1,2). Apparently, saliva is actually composed of two main fluids. Mucous lubricates the mouth, throat, and further pathway of swallowed food. It is also imprisons invading viruses, fungi, and bacteria to prevent otherwise-imminent infections. Serous fluid provides carbohydrate-digesting enzyme amylase. The parotid gland just produces just serous fluid; the sublingual gland just mucous; and the submandibular glands a mixture(1). 
   The Wharton's (submandibular) duct of close to two inches in length dumps the productions of the submandibular glands into the mouth(2). Unstimulated, total saliva production remains about 60-67% in the submandibular glands. Stimulated, saliva production percentage falls off in them and the parotid gland assumes about 50%(3).
   As a vital aside, the oral cavity naturally harbors hundreds of bacteria species, the oral microbiome, either guarding against pathogens (bad bacteria) or causing oral disease. This microbiome is an important thing to keep healthy and has been shown in a study that its health has little to do with genetics. Far more of a role is everyday behavior [think too about all the damage sodas and other unhealthy food and drink can do to teeth in general!]. Saliva is also present on the hands and partly transferred by contact with toothbrushes, coughs, and sneezes among other things. Households tend to influence each other's microbiomes by contact in this manner the most(4).

Sources:
1. "Salivary gland." Wikipedia, The Free Encyclopedia. Updated 22 Sep 2019. Web 8 Oct 2019, https://simple.wikipedia.org/w/index.php?title=Salivary_gland&oldid=6672228.
2. Delf, Jonathan. "The Submandibular Gland." TeachMe Anatomy, TeachMe Series. Updated 22 December 2017, https://teachmeanatomy.info/head/organs/salivary-glands/submandibular/.
3. Wikipedia contributors. "Submandibular gland." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, Updated 13 Mar. 2019. Web. 8 Oct. 2019. https://en.wikipedia.org/wiki/Submandibular_gland.
4. Simmons, Michelle. "Your mouth's role in gut health and immunity: Researchers discover childhood environment has more influence than genetics." Dentistry News, Dentistry News, 5 October 2017, http://www.dentistry.news/2017-10-05-your-mouths-role-in-gut-health-and-immunity-researchers-discover-childhood-environment-has-more-influence-than-genetics.html.
   

   Between the sternum and the heart is an immune system treasure: the thymus. T-cells, critical to respond to invading cells, apparently need some schooling after forming. Especially, they must learn to tolerate the body's own cells. The thymus is this very school. It is especially active and crucial before the teen years(1).
   T-cells specifically earmark viral cells and other invaders for destruction. Zinc is vital to balancing T-cell function and therefore immune system response. Reishi mushroom has been shown to promote "significant beneficial changes in immune cells."(2)

Personal product favorite:
https://shorte.isagenix.com/en-us/products/vitality-well-being/individual/isamune-with-zinc

https://shorte.isagenix.com/en-us/products/vitality-well-being/individual/shake-booster-immune

Sources:
1. "Thymus." Wikipedia, The Free Encyclopedia. 13 Sep 2018. Web 5 Sep 2019. <https://simple.wikipedia.org/w/index.php?title=Thymus&oldid=6250624>.
2. "Why Isamune Plus with Zinc? Just in Time for Winter." Isagenix Health, Isagenix Worldwide, Inc., 3 November 2011, https://www.isagenixhealth.net/just-in-time-for-winter-introducing-new-isamune-plus-with-zinc/.