Cells like neutrophils and monocytes play an important role in which process?

Which of the following is not a type of $T$-lymphocyte?

What is an antibody?

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.

Which is the main physical barrier in our body?

Select the option that contains only secondary lymphoid organs.