In Brief: What are the Immunologic Effects of Ashwagandha?
Recent studies have shown that ashwagandha has strong pleiotropic biological effects related to immune health. These include increasing cytokine levels, CD4, the activity of natural killer cells, phagocytosis, and decreasing IL-4. Overall, it improves the body’s defense against diseases. Additional work in humans is required to establish the mechanisms of how ashwagandha influence different immune cells and thereby, improve immune health.
Ashwagandha is an adaptogen that has bioactive constituents called withanolides. It has been shown to have a range of therapeutic activities, including immunomodulation, fighting infectious agents, enhancing memory, relieving stress, and promoting mental health. 
Studies have shown that ashwagandha may regulate the immune system, enhance the innate immune response to infections, and manage the immune-suppressed diseases. Aswagandha exhibits both immunosuppression, as well as immunostimulatory properties.
The administration of 6ml of ashwagandha root extract to five participants showed a significant increase in the expression of CD4 cells after 96 hours. The natural killer cells also were activated.
The data from two pilot studies showed that the regular consumption of tea fortified with Ayurvedic herbs, including ashwagandha, had enhanced natural killer cells in comparison with a population consuming traditional tea.
The aqueous, alcoholic root extract of ashwagandha significantly increased the levels of Th1 cytokines, decreased IL-4, and increased macrophage functions.
WB365, a combination of Ashwagandha extracts and Maitake mushroom derived glucan, helped to overcome the stress-related inhibition of IL-6, IL-12, and IFN-gamma production.
Another study showed that ashwagandha modulated antioxidant activity, inflammatory cytokines, and induced cell death. The authors suggested it may alleviate cancer cachexia and excessive leukemic cell growth.
A hamster study showed that a combination of ashwagandha with doses of antileishmanial drugs might help in curing leishmaniasis. It also helped in the restoration of the host’s immune response lost due to the disease.
Another animal study showed that ashwagandha, when given with cisplatin, enhanced the antileishmanial efficacy of cisplatin.
In a study, ashwagandha treated mice had increased hemoglobin concentration, red blood count, white blood cell count, and body weight compared to control. The treatment prevented myelosuppression and showed increased antibody responses towards human erythrocytes.
Another study showed that ashwagandha increased nitric oxide production by inducing nitric oxide synthase. The increased nitric oxide production may account for its immunostimulant properties.
In an animal study, ashwagandha had potent inhibitory activity towards the complement system and mitogen-induced lymphocyte proliferation. It, however, did not have any significant effect on humoral immune response in rats.
All these in vivo and animal studies confirm the immunomodulatory properties of ashwagandha. However, more in human randomized controlled trials are required to verify the immunomodulating properties of ashwagandha.
Future studies will determine the mechanisms by which ashwagandha activates immune cells to fight against infections.