Identify $X$ from the given figure.

$A$ substance (low molecular weight protein) produced by host cells in response to viral infection that protects other cells against further viral infection is:

What is vaccination?

$A$ boy happens to put his foot on a rusted nail and the doctor gives him an injection. Most likely,what has the doctor administered?

Define the following terms:
$(a)$ Immunity
$(b)$ Retrovirus
$(c)$ Allergy

The $SCID$ patient has a defective gene for the enzyme Adenosine Deaminase $(ADA)$. He/She lacks functional ...... and therefore,fails to fight the infecting pathogens.