Lung as a Host of Vitamin D Associated Immune Defense Mechanism

• Vitamin D is not merely a micronutrient that plays a role in calcium homeostasis but a pluripotent hormone with extensive immunomodulatory functions. Vitamin D is associated with immunomodulatory effects in our body- this has become an established fact now. Vitamin D insufficiency has been linked to increased risk of infections, in particular viral respiratory tract infection, tuberculosis, obstructive lung diseases like asthma and COPD (HandsdottirSif, 2011).
• How lung acts as a host to Vitamin D associated immune defense mechanism is what we will explore in this blog. Lung immune functions-The respiratory tract has a surface area of approximately 70 m2 and is in direct and continuous contact with the surrounding environment. A local defense system with components of both innate (by birth) and adaptive (acquired during life) immunity has evolved to discriminate between harmful and harmless pathogens and to clear pathogens. Synthesis of active Vitamin D in lungs-The enzyme (1α-hydroxylase) responsible for the activation of Vitamin D is available mostly in our kidneys, but an extra-renal site for Vitamin D synthesis is also found in other immune cells of body out of which one site is the lung cells (alveolar macrophages, dendritic cells, lymphocytes and airway epithelium). This locally formed Vitamin D acts to modulate cell proliferation, cell differentiation and immune function. (John P Bilezikian, 2020)

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• How is vitamin D linked to COVID 19 Infections? Innate immunity or the first line of defense in our body is the primary of our body to handle any pathogenic infection. Post which the adaptive immunity comes into play. Vitamin D helps in activation of various immune cells in our body to fight viral infections by inducing the release of antimicrobial proteins like Cathelicidins and initiates adaptive immune response. Vitamin D is also helpful to curtail cytokine storm. Cytokine storm results from the chronic activation of the innate immune system in which the inflammatory cytokines are released at a rate higher than normal and starts killing healthy cells in our body. Vitamin D helps in inhibition of various mediators which are involved in this process to control the rogue response of body in the form of this cytokine storm.
• Epidemiological and mechanistic studies indicate that vitamin D may play an important role in the development of respiratory diseases including COVID 19. A large number of clinical trials are being registered to investigate the effect of Vitamin D on various COVID 19 outcomes. Until the results of these trials are known, a prudent, general health measure is to ensure vitamin D sufficiency.