A 10-month-old boy is brought to the office due to recurrent sinopulmonary infections for the last several months. The infections were caused by encapsulated bacteria, and the patient was also recently hospitalized due to Pneumocystis jiroveci pneumonia. He was born at full term after an uneventful pregnancy. Family history is significant for a maternal uncle's early childhood death due to severe infection. Genetic testing of the patient reveals missense mutation of the CD40 ligand gene. Interaction between which of the following immune components is most likely impaired in this patient?

Question

A 10-month-old boy is brought to the office due to recurrent sinopulmonary infections for the last several months.  The infections were caused by encapsulated bacteria, and the patient was also recently hospitalized due to Pneumocystis jiroveci pneumonia.  He was born at full term after an uneventful pregnancy.  Family history is significant for a maternal uncle's early childhood death due to severe infection.  Genetic testing of the patient reveals missense mutation of the CD40 ligand gene.  Interaction between which of the following immune components is most likely impaired in this patient?

Quizplus · Accepted Answer

Eductional Objective: CD40-ligand (CD40L) is expressed primarily on activated T cells.  It binds to CD40 on antigen-presenting cells, including B cells, leading to their full activation (costimulation).  Therefore, CD40L plays a vital role in both the cell-mediated and humoral immune response.

A 10-Month-Old Boy Is Brought to the Office Due to Recurrent