A mother takes her son to the doctor and describes the following symptoms that she has observed. The child is running a fever, has flu-like symptoms, and his lymph glands are very swollen and sore to...

A mother takes her son to the doctor and describes the following symptoms that she has observed. The child is running a fever, has flu-like symptoms, and his lymph glands are very swollen and sore to the touch. The mother herself has a history of lymph node problems. She had a mastectomy that included the removal of axillary lymph nodes on her left side. She was also a patient of this practice on one of her follow-up visits.

The mother wants to know what caused her son's swollen and sore lymph glands.
What reasons would you give to help the mother understand why these signs and symptoms
have occurred?