Viruses infect host cells. By the induction of viruses,the host cells produce which of the following?

Which of the following is a physiological barrier?

In higher vertebrates,the immune system can distinguish self-cells and non-self. If this property is lost due to genetic abnormality and it attacks self-cells,then it leads to

What type of immunity is provided by the treatment given against snake bites?

The lack of $B$-cells and $T$-cells is known as:

Which of the following provides the microenvironment for the maturation of $T$-lymphocytes?