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Infection and Immunity, June 2003, p. 3349-3356, Vol. 71, No. 6
0019-9567/03/$08.00+0 DOI: 10.1128/IAI.71.6.3349-3356.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Department of Molecular and Cellular Pathology, University of DundeeNinewells Hospital Medical School, Dundee DD1 9SY,1 Department of Clinical Biochemistry and Immunology, Leeds General Infirmary, Leeds LS1 3EX, United Kingdom2
Received 9 December 2002/ Returned for modification 24 January 2003/ Accepted 24 February 2003
The cleavage of human serum monomeric immunoglobulin A1 (IgA1) and human secretory IgA1 (S-IgA1) by IgA1 proteinase of Neisseria meningitidis and cleavage by the proteinase from Proteus mirabilis have been compared. For serum IgA1, both proteinases cleaved only the
chain. N. meningitidis proteinase cleaved only in the hinge. P. mirabilis proteinase sequentially removed the tailpiece, the CH3 domain, and the CH2 domain. The cleavage of S-IgA1 by N. meningitidis proteinase occurred only in the hinge and was as rapid as that of serum IgA1. P. mirabilis proteinase predominantly cleaved the secretory component (SC) of S-IgA1. The SC of S-IgA1, whether cleaved or not, appeared to protect the
1 chain. Purified Fc fragment derived from the cleavage of serum IgA1 by N. meningitidis proteinase stimulated a respiratory burst in neutrophils through Fc
receptors, whereas the (Fc
1)2-SC fragment from digested S-IgA1 did not. The loss of the tailpiece from serum IgA1 treated with P. mirabilis proteinase had little effect, but the loss of the CH3 domain was concurrent with a rapid loss in the ability to bind to Fc
receptors. S-IgA1 treated with P. mirabilis proteinase under the same conditions retained the ability to bind to Fc
receptors. The results are consistent with the Fc
receptor binding site being at the CH2-CH3 interface. These data shed further light on the structure of S-IgA1 and indicate that the binding site for the Fc
receptor in S-IgA is protected by SC, thus prolonging its ability to activate phagocytic cells at the mucosal surface.
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