How many heavy polypeptide chains are present in each antibody molecule?

Differentiate between $T$-lymphocytes and $B$-lymphocytes.

Which cells help $B$-cells in the production of antibodies?

What is vaccination?

Before and after organ transplantation,it is necessary to perform:

Assertion: Artificially acquired passive immunity results when antibodies or lymphocytes produced outside the host are introduced into a host.
Reason: $A$ bone marrow transplant given to a patient with genetic immunodeficiency is an example of artificially acquired passive immunity.