Billy DeWitt was a normal, full-term baby at birth. Beginning at...

Billy DeWitt was a normal, full-term baby at birth. Beginning at about 10 months of age, Billy suffered from a series of infectious processes such as sinusitis, otitis media, and pneumonia. All of these conditions were successfully treated with antibiotics, but within a few weeks of the resolution of one infection, another would occur.

Now at about four years of age, Billy is examined by a pediatrician who notes that Billy lacks palatine tonsils, although he does not have a history of tonsillectomy. Questioning of Billy's mother reveals that she had two male relatives who died in infancy from infectious disease. The physician orders laboratory tests that reveal that the quantity of immunoglobin in Billy's serum is about one-fifth of normal, and that there is a marked deficiency in the number of circulating B-lymphocytes in Billy's blood. Tests to determine the functional state of Billy's T-lymphocytes are all normal.

Billy is diagnosed with a genetic disorder called X-linked agammaglobulinema. He begins a monthly intravenous injection of gamma globulin which he will need to continue for the rest of his life. Billy should no longer suffer recurrent infections and should develop physically and mentally as a normal child. Aside from receiving monthly injections of gamma globulin, he should lead a normal life now that this course of treatment is in place.

What part of Billy's adaptive immune response is disrupted by this disorder?  How can we classify the adaptive immunity provided by the monthly injections of immunoglobulins?