They can actually bind onto antigens found on cell membranes of bacterial cells or infected cells and that can essentially destroy those pathogens when these cells bind onto them. So we have four different types of T lymphocytes or T cells. So we have helper T cells, killer T cells, memory T cells and suppressor T cells. So let's begin with the helper T cells. So helper T cells basically release special types of chemicals into the surrounding blood or the surrounding lymph and they help other cells, other immune cells, actually mature into their specialized form and we'll talk more about that in the next several lectures. We also have killer T cells, not to be confused with natural killer cells.