Due to a history of recurrent infections and suspected humoral immune deficiency, quantitative measurement of total serum immunoglobulin was performed showing markedly reduced IgG-concentration (IgG: 571 mg/dl (700–1600); IgA 205 mg/dl (70–400); IgM: 75 mg/dl (40–230)) consistent with diagnosis of unclassified antibody deficiency. Here, CD40LG is linked to infection.