Antigen is a substance which

Lymph glands and nodes help to

What is produced by sensitized helper $T$-cells?

Assertion $A$: Vaccination protects an individual against infection by specific pathogens.
Reason $R$: $B$ and $T$ memory cells produce antibodies in large quantities to neutralize the pathogen attack.
Which option is correct for Assertion $A$ and Reason $R$?

Grafting between two members of the same species is known as:

Long-term immunity against pathogens is provided by which of the following?