Antibodies fight against:

What is primary immune response?

When children without $T-$ cells and $B-$ cells are kept in germ-free isolation suits,the disease is known as:

Given below are two statements:
Statement $I$: Bone marrow is the main lymphoid organ where all blood cells including lymphocytes are produced.
Statement $II$: Both bone marrow and thymus provide micro-environments for the development and maturation of $T$-lymphocytes.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following checks is $NOT$ required for organ transplantation?

Identify the cell that enables the human body to distinguish between self and non-self.