What is it called when the body attacks its own cells,causing damage to the body?

Which one of the following options gives the correct categorization of lymphocytes according to formation,maturation,and type of immunity?

Along with lymphoid organs,$WBCs$ are also present within the mucosa of digestive,respiratory,and excretory tracts as $MALT$,which constitutes about $.......$ of the total lymphoid tissue of the body: (in $\%$)

Vaccination against measles means.........

Provide definitions/explanations for the following terms: $1$. Retrovirus,$2$. Antibody.

$A$ mammal born without a thymus gland is unable to produce which of the following?