Selective Antibody Deficiency and Recurrent Pneumococcal Bacteremia in a Patient with Sjögren's Syndrome, Hyperimmunoglobulinemia G, and Deficiencies of IgG2 and IgG4

Antibodies specific for capsular polysaccharides of Streptococcus pneumoniae enhance complement fixation via the classical pathway and thereby initiate the single most efficient mechanism for opsonization of these organisms.1 Since most IgG antibodies against polysaccharide antigens are of the IgG2 subclass,2 3 4 which is believed to activate complement poorly,5 , 6 the relative protective efficiency of IgG as compared with IgM antipneumococcal antibodies is of great interest, especially in view of the practice of passive immunization with IgG preparations. This question has hardly been addressed in human beings,7 , 8 and experimental data from animal models are controversial.8 9 10 11 Bacteremic pneumococcal disease continues to carry a poor . . .