Which cells secrete interferons?

Grafting of tissue or organ between individuals of different species is called

The immunity developed in the body after recovering from a disease is:

Resistance against pathogens is due to

What is true about $T-lymphocytes$ in mammals?

Given below are two statements. Select the most appropriate answer from the given options.
Statement-$I$: $T$-lymphocytes have $4$ subtypes as helper,killer,memory,and suppressor $T$-cells.
Statement-$II$: $B$-lymphocytes mature in the thymus and are responsible for cell-mediated immunity.