Which of the following organs is a primary lymphoid organ?

What is an antigen?

What is immunity based on?

Read the following statements and choose the correct set of statements $:$
$(a)$ Cell-mediated immune response is responsible for the graft rejection.
$(b)$ Grafts from just any source $-$ an animal,another primate,or any human beings can be made since the grafts would be accepted sooner or later.
$(c)$ The organs cannot be taken from just anybody for transplant.
$(d)$ Tissue matching,blood group matching are essential before undertaking any graft/transplant.
Choose the correct answer from the options given below $:$

In the structure of an antibody,the heavy chains and light chains are held together by which type of bond?

Helper $T$-cells : Lymphokines :: Killer $T$-cells : . . . . . . .