The primary function of the immune system is to defend the body against invaders (i.e. viruses, bacteria, foreign substances) that could potentially cause harm or illness. The immune system is not just a group of organs like some other body systems; rather, it is a network of white blood cells, antibodies, and other substances that pervade the body, and it also includes parts of other organs such as the thymus, bone marrow, spleen, lymph nodes, and liver [1]. Critical to proper immune system function is the body’s ability to recognize the difference between its own cells and foreign invaders.
The main types of immunity are nonspecific (innate) and specific (adaptive) [2]. Nonspecific, or innate, immunity is present at birth and is a more general defense. Innate immunity also involves circulating white blood cells and plays a critical role in acute inflammation. Specific, or adaptive, immunity is acquired throughout life and changes over time as the body learns responses to different antigens it encounters; it elicits a more precise response than nonspecific immunity.
How Does CBD Affect the Immune System?
Cannabidiol (CBD) has recently been shown to have potentially beneficial effects on both innate and adaptive immunity [3]. It has demonstrated abilities to be both immunosuppressive and neuroprotective [3]. Because the immune system evokes responses through various cell types, the mechanisms through which CBD acts varies. The term “immunosuppressive” sounds deceptively negative when, in this case, it refers
to tamping down immune responses that are excessive or overactive, which can ultimately lead to damage.
The main immunosuppression action seen with CBD use is an anti-inflammatory effect. The anti-inflammatory effect most likely occurs through multiple mechanisms involving cytokines, which are nervous system messenger proteins that allow for communication between the innate and adaptive immune systems and are heavily involved in inflammation [2] [4]. CBD has demonstrated an ability to inhibit proinflammatory effects by both inhibiting cytokines and suppressing cytokine production from different cell types [2].
Because nervous tissue regenerates poorly, the neuroprotective effects of CBD can be highly beneficial in preventing such tissues from breaking down or becoming irreparably damaged. Microglial cells function as immune cells in the central nervous system (CNS) and, when functioning properly, monitor and maintain the health of neurons. However, when microglial cells are overactive, they cause excessive inflammation that leads to neurodegeneration [5]. Experimentally, CBD has shown the ability to inhibit proliferation of and induce cell death of microglial cells [5]. Important to note is that these effects are discriminatory and only occur when microglial cells are overactive or too numerous; microglial cells functioning healthily and properly are not targeted. In one example, CBD was shown to decrease microglial accumulation in diabetic mice [6]. This example showed potential for use of CBD in the treatment of autoimmune disorders. The targeting of overactive microglial cells by CBD is controlled through more complicated pathways within the CNS.
Previously, we discussed the potential use of CBD in treatment of equine recurrent uveitis (ERU) and also examined the capacity of CBD and another cannabinoid, cannabigerol (CBG), to produce anti-inflammatory effects in cases of osteoarthritis (OA). Both of these diseases are considered autoimmune disorders, which occur when a body either fails to recognize its own cells as nonharmful or produces an excessive immune response as a reaction to nonharmful substances. In cases of ERU, CBD exhibited potent antioxidant properties that reduced oxidative stress; this reduced inflammation and also prevented degeneration of the eye [7]. Meanwhile, a study conducted by Reyad Elbarbary and Fadia Kamal at Penn State College of Medicine showed that treatment with either the CBD or CBG oil significantly reduced the thickness of the synovial membrane, which indicated possible anti-inflammatory effects [8]. For more information about cannabinoids as potential treatments for these autoimmune disorders, please check out our other articles.
In addition to being immunosuppressive and neuroprotective, CBD has also demonstrated the capacity to enhance some immune system effects. The intricate pathways and regulation of signaling within the immune system allow this one molecule to elicit different effects within the same system. CBD can increase the concentration of intracellular calcium, which is the most well-known way in which CBD enhances immune responses [9]. The increased intracellular calcium contributes to the activation of mast cells and basophils, which are white blood cells that contain enzymes that are released during an allergic response to foreign substances or during a general immune response to presence of bacteria or parasites [2]. It also contributes to neutrophil degranulation, which is the process by which white blood cells quickly release substances that kill off harmful bacteria [10]. The immune system pervades the body and regulates body functions through intricate and intertwined pathways, and further research is required to fully understand the mechanisms by which CBD produces both immunosuppressive and immune system enhancing effects.
The immune systems of animals are complex, tightly regulated, and critical to overall health and function. The combination of immunosuppressive, neuroprotective, and immune system-enhancing effects of CBD make it an attractive potential candidate not only for maintenance of homeostasis in healthy animals but also for treatment of autoimmune disorders such as diabetes, multiple sclerosis (MS), ERU, and OA.
Conclusion:
A healthy immune system is critical to the well-being of all animals, including horses. Cannabidiol (CBD) has the ability to exploit the intricate mechanisms within the immune system to elicit immunosuppressive, neuroprotective, and immune system-enhancing effects. These effects make CBD potentially beneficial for healthy animals as well as animals with autoimmune disorders. Animals demonstrate two main types of immunity: 1) innate immunity that provides general defense, and 2) adaptive immunity that is acquired throughout life. CBD has shown the potential to elicit effects on both innate and adaptive immunity by acting on proteins that serve as messengers between the two systems. The primary and most well researched effect of CBD in the immune system is an anti-inflammatory effect, which contributes to both immunosuppression and neuroprotection. It also demonstrated neuroprotective properties by inhibiting overactive microglial cells that cause neurodegeneration to occur too rapidly. CBD can also enhance immune system effects by increasing the amount of intracellular calcium, which stimulates specific white blood cells to defend the body from harmful invaders.
References
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- (2) Marshall, J.S., Warrington, R., Watson, W. et al. An introduction to immunology and immunopathology. Allergy Asthma Clin Immunol 14 (Suppl 2), 49 (2018).
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