Which organs provide the microenvironment for the maturation of $T$-lymphocytes?

Match the following columns correctly:

Column-$I$	Column-$II$
$(a)$ Physical barrier	$(w)$ Saliva
$(b)$ Physiological barrier	$(x)$ Interferons
$(c)$ Cellular barrier	$(y)$ Skin
$(d)$ Cytokine barrier	$(z)$ Monocytes

How many types of memory cells are there in the immune system?

Fill in the blanks: Our body, when it encounters a pathogen for the first time, produces a response called . . . . . . $a$ . . . . . . response, which is of . . . . . . $b$ . . . . . . intensity. Subsequent encounters with the same pathogen elicit a . . . . . . $c$ . . . . . . intensified . . . . . . $d$ . . . . . . response.

Plasma cells are derived from

When ready-made $ antibodies $ are directly given to protect the body against foreign agents, it is called passive immunity.