Question

What is true about T-Lymphocytes in mammals : -
A) There are three main types-cytotoxic T-cells, helper T-cells and suppressor T-cells
B) These originate in lymphoid tissues
C) They scavenge damaged cells and cellular debris
D) These are produced in thyroid

Answer 1

Lymphocytes have functions like secretion of cytokines, antigen representation and suppression of immune activity against self antigens in the body. The cytotoxic T cells resemble natural killer cells which attack the foreign body as fast as it is possible.

Complete answer:
Lymphocytes are blood cells which are made in bone marrow. They are an important part of the immune system. The immune system is the complex network of communicating immune cells. The lymph organs are spleen, tonsils, lymphoid tissue, etc.
There are two types of lymphocytes : T lymphocytes and B lymphocytes. T cells are matured in thymus. The T cells which kill the foreign body directly with CD8+ receptor are called killer cells which are cytotoxic in nature. The T cells which show indirect immune response by secreting cytokines are called helper T cells .The cells that suppress the immune reaction against their own cells are called regulatory or suppressing cells.
So, the primary and secondary immune responses are carried out by B and T lymphocytes.B lymphocytes produce proteins known as antibodies to kill pathogens while T lymphocytes help B lymphocytes to produce antibodies.The T lymphocyte mediates cell mediated immunity.

The correct option is A.

Additional information
Cyclosporin kills T cells and thus lowers the immunity. Thus it acts as an immunosuppressant and is used during any transplantation to avoid graft rejection.

Note:
Natural Killer T cells (NKT) are not the same as innate killer cells. They can work by MHC (Major Histocompatibility complex) representation like Tc cells or secretion of cytokines like cells.