Fig. 2.

The functional roles mediated by interactions of chemokines with receptors expressed on immune cells. The RNA-seq data were derived from HPA. The relative mRNA expression of chemokines (left hand columns) and receptors (upper right-hand columns) in selected immune cells is shown in the heatmap, with the color based on their transcript per million (TPM) values. The inflammatory and homeostatic chemokines and receptors are shown in red and green, respectively. Chemokines with dual functions are indicated in blue [11, 14, 18, 46]. Chemokine receptors with dual functions are classified into inflammatory families [14]; for example, CCR10/CCL27-CCL28 have been shown to have homeostatic functions [11, 46, 352–354], and several mechanisms have been reported to be involved in inflammation [354]. The atypical chemokine receptors are shown in black. For instance, the platelet chemokine PF4/CXCL4 is quickly released as the first-line inflammatory mediator upon vascular injury and platelet activation. PF4 is also secreted by a variety of immune cells and has also been implicated in the pathology of a variety of inflammatory and autoimmune diseases and cancer [11, 355]. The association of chemokines with receptors was analyzed using STRING (https://string-db.org/), and their interaction networks identified based on the STRING analysis and published reviews [11, 14, 18, 46] are shown in the lower-right hand table, highlighted in purple