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.
There are two basic types of T lymphocytes: T-helper cells (CD4+ cells) and T-cytotoxic cells (CD8+ cells). When activated, the T-cytotoxic cells can eliminate the host cells that are infected with virus, Mycobacteria, certain intracellular bacteria, fungi, parasites, and tumor cells.