$T$-cells mature in the . . . . . . .

Match the columns:

Column-$I$	Column-$II$
$(a)$ Physical barrier	$(1)$ Skin
$(b)$ Physiological barrier	$(2)$ Interferon protein
$(c)$ Cellular barrier	$(3)$ Leucocytes
$(d)$ Cytokine barrier	$(4)$ Saliva in the mouth

Person '$A$' cannot step out of his house. He has to spend his entire life in sterile isolation; otherwise, he would quickly contract a fatal infection. This person has almost no effective immune system. This disease is also called '$baby$ $in$ $a$ $bubble$ $syndrome$'. Identify the disease this person '$A$' is suffering from.

Identify the barrier of innate immunity in which virus-infected cells secrete proteins called interferons.

Passive immunity was discovered by

What causes immunodeficiency?