What is true about T-lymphocytes in mammals?

1. These are produced in thyroid
2. There are three main types — cytotoxic T-cells, helper T-cells and suppressor T-cells
3. These originate in lymphoid tissues
4. They scavenge damaged cells and cellular debris

The lymphocytes which differentiate in the thymus are known as the T-lymphocytes. T-lymphocytes are responsible for the cellular immune response.