Pneumococcal capsular polysaccharide-specific IgA triggers efficient neutrophil effector functions via Fc alpha RI (CD89)

Specific anti-capsular polysaccharide IgG is believed to be important for p rotection against infection by Streptococcus pneumoniae. Significant IgA re sponses have been observed after vaccination with pneumococcal vaccines, bu t the role of this isotype in anti-pneumococcal host defense is unclear. He re, it is shown that purified serum IgA specific for pneumococcal capsular polysaccharides can initiate efficient cellular effector functions, such as phagocytosis, via interaction with the myeloid IgA receptor, Fc alpha RI ( CD89), The efficiency of Fc alpha R-triggered granulocyte effector function s was comparable to that of Fc gamma RIIa (CD32), as shown in experiments w ith bispecific antibodies. These results support a role for polysaccharide- specific IgA in antipneumococcal cellular effector function and suggest tha t Fc alpha RI represents an important leukocyte receptor for immunity again st S. pneumoniae.