After an organ transplant from an unrelated donor,which of the following plays the lead role in graft rejection?

Identify the correct statement$(s)$ regarding the human immune system.

The cells which directly attack and destroy the antigens are known as

Which of the following is not related to passive resistance?

Many vertebrates produce virus-resistant substances that inhibit viral replication. What are these substances known as?

In an antibody,disulphide bonds are present . . . . . .
$i$. between two heavy chains
$ii$. between two light chains
$iii$. between the constant region of a light chain and the constant region of a heavy chain
$iv$. between antigen binding sites of both the heavy and light chains
$v$. between the variable region of a light chain and that of a heavy chain
Select the correct answer from the options given below.