Unlike the rest of the cells in your body, your red blood cells lack nuclei. That quirk dates back to the time when mammals began to evolve. Other vertebrates such as fish, reptiles, and birds, have red cells that contain nuclei that are inactive. Losing the nucleus enables the red blood cell to contain more oxygen-carrying hemoglobin, thus enabling more oxygen to be transported in the blood and boosting our metabolism.

A cellular protein that helps guide immune cells to the gut has been newly identified as a target of HIV when the virus begins its assault on the body's immune system, according to researchers from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH).