Secretion of interferon is which type of barrier?

Which of the following cells are involved in the defence mechanism of the body?

Which of the following are types of immunity?

Consider the following four statements $(i-iv)$ regarding kidney transplantation and select the two correct ones.
$(i)$ Even if a kidney transplant is successful,the recipient needs to take immunosuppressants for a long time.
$(ii)$ Cell-mediated immune response is responsible for the rejection of the graft.
$(iii)$ $B$-lymphocytes are responsible for the rejection of the graft.
$(iv)$ The acceptance or rejection of a transplanted kidney depends on specific interferons.

Which one of the following groups is associated with secondary lymphoid organs?

Define and explain: Active immunity and Passive immunity.