T lymphocytes or T-cells

T lymphocytes play a key role in the adaptive immune system. There are two main types of T lymphocytes. 

• Cytotoxic T lymphocytes are responsible for directly attacking and killing virus-infected cells and cancerous or tumor cells. 
• Helper T lymphocytes are responsible for regulating the body’s immune system response by helping cytotoxic T lymphocytes and B lymphocytes in eliminating invading microbes.

B lymphocytes or B-cells

B lymphocytes are primarily responsible for creating antibodies, a type of protein that targets bacteria, viruses, and other intruding microbes. The antibodies created by B lymphocytes work by binding to invading pathogens, thus preventing them from entering a normal cell and causing infection. B cells can also recruit other cells to help eliminate infected cells.