Serologic tests were negative for acute Epstein-Barr virus infection (capsid IgM negative 23.2 [ref <36.00], early IgG negative <5.00 [ref <9.00], capsid IgG positive 649.00 [ref <18.00], nuclear antigen positive 145.00 [ref <18.00], indicative of past infection), cytomegalovirus (IgM negative 9.26 [ref <30.00], IgG negative <0.2 [ref <0.6]), and Bartonella henselae (IgM negative <1:20 [ref <1:20], IgG negative <1:128 [ref <1:128]). Here, CD40LG is linked to Epstein-Barr virus infection.