Caffeine:
Various studies have demonstrated that caffeine can modulate different
aspects of innate and adaptive immunity. Caffeine has been shown to
affect cytokine production, free radical production, lymphocyte
proliferation, antibody production, natural killer cell function,
histamine release, and immune cell apoptosis
(Horrigan et al. 2006). Myeloperoxidases
are essential for the antimicrobial activity during neutrophil’s
respiratory burst, and in vitro studies showed that caffeine
significantly increases the release of myeloperoxidase from a mixed
population of neutrophils and PBMC
(Sullivan et al. 1995). As a reduction
of neutrophils was observed in the peripheral blood of COVID-19 patients
(Liu et al. 2020), the enhancement of
myeloperoxidase activity by caffeine could potentially improve COVID-19
disease condition. In line with caffeine’s role in immunomodulation, an
intriguing study reported that a bolus dose of 6 mg/kg caffeine caused
an increase in total lymphocyte count and an increase in CD8+ T cell
count (Bishop et al. 2005). The same study
also reported that an increase of CD4+CD69+ T cells before and after
exercise with pre-exercise caffeine ingestion only
(Bishop et al. 2005). Therefore, it shows
the immune stimulatory role of caffeine on T cells. Furthermore, a
reduction in lymphocytes and CD8+ positive T cells in the peripheral
blood of COVID-19 patients (Liu et al.
2020) means that caffeine may have the potential to increase the CD8+ T
cells as well as the other cytotoxic CD4+CD69+ T cells in these patients
and alleviate COVID-19 related symptoms by immune modulation