Gregor Mendel, in full Gregor Johann Mendel, original name (until 1843) Johann Mendel, (born July 22, 1822, Heinzendorf, Silesia, Austrian Empire [now Hynčice, Czech Republic]—died January 6, 1884, Brünn, Austria-Hungary [now Brno, Czech Republic]), botanist, teacher, and Augustinian prelate, the first person to lay the mathematical foundation of the science of genetics, in what came to be called Mendelism.
In cases of immune system overactivity, the body attacks and damages its own tissues (autoimmune diseases). Immune deficiency diseases decrease the body's ability to fight invaders, causing vulnerability to infections.