CD4 and autoimmune disease: Figure 1 illustrates the main immunomodulatory effects of P4. This specific immunosuppressive action of P4 is associated with the inhibition of the Th1 and Th17 pathways, which can shorten the active course of some chronical autoimmune diseases, such as rheumatoid arthritis and multiple sclerosis [65]. Hormone replacement therapy (HRT) can also be an example of the anti-inflammatory action of P4 since this hormone reverses the menopausal CD4/CD8 ratio, as well as limits the general peri- and postmenopausal inflammatory state [66].