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.
helper T cell. helper T cell n. Any of a class of T cells that are activated by interacting with antigen-presenting cells, such as a dendritic cells, and then function to activate other cells of the immune system, including B cells, cytotoxic T lymphocytes, and phagocytes. Activated helper T cells usually have CD4 receptors on the surface. Also called T-helper cell. helper T cell n.