**1. Introduction**

Erythrocytes provide oxygen and other necessary compounds to cells of the vascular compartment and other cells of the body. Erythrocytes also provide protection by collaborating in many ways with immune cells and humoral immunity [1, 2]. Erythrocytes communicate with other parts of the vascular compartment and to some extent also other parts of the body (**Figure 1**). Erythrocytes communicate as a transporter or by using signaling components perceived by receptors in other cells. We give some examples of how erythrocytes use magnesium and selenium in a hierarchy for optimal results as part of this communication. Magnesium occurs together with ATP, the energy currency of erythrocytes, and other cells. This makes magnesium necessary for many enzymes like the kinases of glycolysis. Further examples will be taken from lipids, glutathione, sphingosine-1-phosphate, purinergic signaling, RNA, the malaria parasite Plasmodium, and erythrocyte microvesicles.

#### **Figure 1.**

*Communication between erythrocytes and other cells takes place through RNA, proteins, metal ions, and other compounds that each form hierarchies. The first hierarchy involves free radical-induced production of compounds where hydroxyl radical and solvated electron reactions are involved. The second hierarchy involves electrophilic and nucleophilic compounds forming products adequate to the cells. The third hierarchy involves metal ions and ligands dependent on the previous two hierarchies but adapted to cell demand. In erythroid precursors and in other cells, excluding the erythrocyte, compounds and metal ions may reach DNA and RNA not controlled by evolutionary developed genome adapted to cell demand. Small changes of DNA and RNA, including epigenetic changes, may take place. These may become established or restored, but large damages will present symptoms and are difficult to restore.*
