Which cells do not produce antibodies but help $B$-cells in the production of antibodies?

Which of the following is $NOT$ included in physiological barriers?

Which cells are responsible for acquired immunity?

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 $:$

Which of the following is not a secondary lymphoid organ?

Which of the following is an example of passive immunity?