A common problem for the purple leaf plum tree is blossom blight, in which first the flowers, then young leaves, turn brown and wither, according to Grow Fruit by Alan Buckingham.
Once activated, helper T cells start to divide and to produce proteins that activate B and T cells as well as other immune cells. The killer T cell is specialized in attacking cells of the body infected by viruses and sometimes also by bacteria.
B lymphocytes are powerless to penetrate the cell so the job of attacking these target cells is left to T lymphocytes. T lymphocytes are cells that are programmed to recognize, respond to and remember antigens. T lymphocytes (or T cells) contribute to the immune defenses in two major ways.