Bitter Taste Receptors Found on Neutrophils: Our sense of taste might relate to the ability of our white blood cells to detect and respond to pathogens.
May 4, 2015. As we continue to build more biology-centric networks, we ran into this one. Humans have (at least) 28 Taste Receptors, G protein coupled receptors for sweet, umami and bitter taste. TAS1Rs are thought to sense sweet and glutamate (umami), whereas the shorter TAS2Rs are responsible for detecting bitter taste. While bitter taste receptors are thought to be specifically expressed on the taste papillae (buds) of the tongue, our analysis found an unmistakable signature for 22 of the TAS2R bitter taste receptors on blood neutrophils, as defined by neutrophil gene ELANE (FIGURE 1). TAS1R3 was linked to a distinct set of blood cells: CD8A postive T lymphocytes, NK cells (defined by KIR2DL3) and CD68 positive macrophages. Consistent with this observation, a February 2015 publication reported the discovery of taste receptors on leukocytes, and a 2014 paper reported umami receptors on neutrophils.
FIGURE 1
The implications of this observation are uncertain. However, recent work has identified bitter taste receptors as bacterial chemosensors in lung airway epithelium. In addition, a variant in one bitter taste receptor was linked to susceptibility to respiratory infection. Perhaps it's not surprising that this mechanism might extend to our white blood cells, enabling them to use these chemical receptors to sense and seek out foreign invaders such as pathogenic bacteria. We are curious to hear from the innate immunity & chemoreception communities on this.
This observation also highlights one of the limitations of the Molquant tools. Because our datasets do not contain any tongue samples, we are unable to identify the presence of these receptors on tongue papillae. If these receptors represented previously uncharacterized biology, we would mistakenly conclude that these GPCRs were specifically expressed in neutrophils. We look forward to the increasing size and diversity of available samples to improve the networks.