Absent B cells.Low serum IgG (358 mg/dL; RV: 639-1349**) and IgM (59 mg/dL; RV: 56-352**), with elevated oligoclonal IgA (497 mg/dL; RV: 70-312**). Decreased specific anti-polisacaridic antibodies after vaccination.Recurrent pneumonias, oral ulcers and odynophagia. Here, CD40LG is linked to pneumonia.