CD40LG and Klebsiella Infections: IgG2 deficiencies have been associated with increased susceptibility to certain bacterial infections [41]; and Alsaedi et al. [42] recently reported IgG2 deficiency and low IgM in a human patient presenting recurrent HMV K. pneumoniae bacteremia in the absence of pyogenic liver abscess or other localized metastatic Klebsiella infection.