$WBC$ is an example of

An antibody is:

Which of the following organs are primary lymphoid organs?

Define the following terms: Antigen and Lymphoid organs.

Given below are two statements:
Statement $I:$ Autoimmune disorder is a condition where the body's defense mechanism recognizes its own cells as foreign bodies.
Statement $II:$ Rheumatoid arthritis is a condition where the body does not attack self-cells.
In the light of the above statements,choose the most appropriate answer from the options given below:

Introduction of attenuated pathogens in human body results in . . . . . . .