Which cells are involved in the immune response?

Except for the skin,other physical barriers that also help to prevent the entry of microorganisms are:
$I.$ Mucus coating of the epithelium lining the respiratory tract
$II.$ Gastrointestinal tract
$III.$ Urogenital tract
Choose the correct option.

Some people who have suffered from a disease may not be affected again during their lifetime; such immunity is called

Which types of cells are produced during the clonal selection of $B$-cells?

Which of the following is an autoimmune disorder?

Define and explain the functions of $B$-lymphocytes and $T$-lymphocytes.