Phytosterols are steroid compounds present in plants which are similar to cholesterol in structure and functions. Several animal and human studies show that phytosterols lower plasma total and LDL-cholesterol levels. It is generally accepted that cholesterol-lowering effect of phytosterols is due to direct inhibition of cholesterol absorption, through displacement of cholesterol from mixed micelles. Saturated phytosterols (stanols) are found to be more efficient in lowering cholesterol levels than sterols (unsaturated). Phytosterols are structurally very similar to cholesterol except that they always contain some substitutions at the C24 position on the sterol side chain. Plasma phytosterol levels in mammalian tissues are normally very low due to poor absorption from the intestine and faster excretion from the liver compared to cholesterol. Phytosterols can be metabolized in the liver of mammals into C21 bile acids instead of the normal C24 bile acids. Phytosterols may produce health benefits in animals/humans such as reduction of cholesterol levels with decreased risk of coronary heart diseases, anti-inflammatory activities, induction of apoptosis in cancer cells, disease prevention and treatment. However, few adverse effects of phytosterols occur in small group of individuals with phytosterolemia, an inherited lipid disorder and they may cause decrease in plasma levels of nutrients such as carotenoids. In conclusion, phytosterols and their derivatives have several biological activities which promote the health of man and animals, so their consumption should be encouraged in the population.

Oxysterols are the products of cholesterol oxidation. They have a wide range of effects on several cells, organs, and systems in the body. Oxysterols also have an influence on the physiology of the immune system, from immune cell maturation and migration to innate and humoral immune responses. In this regard, oxysterols have been involved in several diseases that have an immune component, from autoimmune and neurodegenerative diseases to inflammatory diseases, atherosclerosis, and cancer. Here, we review data on the participation of oxysterols, mainly 25-hydroxycholesterol and 7α,25-dihydroxycholesterol, in the immune system and related diseases. The effects of these oxysterols and main oxysterol receptors, LXR and EBI2, in cells of the immune system (B cells, T cells, macrophages, dendritic cells, oligodendrocytes, and astrocytes), and in immune-related diseases, such as neurodegenerative diseases, intestinal diseases, cancer, respiratory diseases, and atherosclerosis, are discussed.