Tumor-associated and microbial proteases compromise host IgG effector functions by a single cleavage proximal to the hinge.

Brezski RJ, Vafa O, Petrone D, Tam SH, Powers G, Ryan MH, Luongo JL, Oberholtzer A, Knight DM, Jordan RE
Proc Natl Acad Sci U S A. 2009 106 (42): 17864-9

PMID: 19815504 · PMCID: PMC2758810 · DOI:10.1073/pnas.0904174106

The successful elimination of pathogenic cells and microorganisms by the humoral immune system relies on effective interactions between host immunoglobulins and Fc gamma receptors on effector cells, in addition to the complement system. Essential Ig motifs that direct those interactions reside within the conserved IgG lower hinge/CH2 interface. We noted that a group of tumor-related and microbial proteases cleaved human IgG1s in that region, and the "nick" of just one of the heavy chains profoundly inhibited IgG1 effector functions. We focused on IgG1 monoclonal antibodies (mAbs) since IgG1 is the most abundant human subclass and demonstrates robust Fc-mediated effector functions. The loss of Fc-mediated cell killing activities was correlated with diminished binding to the Fc gamma family of receptors, but a similar decrease in affinity was not observed toward the FcRn receptor that maintains IgG in circulation. Endogenous human IgG cleavage products of comparable size to mAbs with the single cleavage were detected by Western blot analysis in synovial fluid from patients with rheumatoid arthritis and in breast carcinoma extracts. Their detection is problematic under physiological conditions, since there is no loss of structure, and antigen-binding capability is unaffected. These findings suggest that within the hostile proteolytic microenvironments associated with many diseases, key effector functions of host IgGs, or therapeutic Abs, may be compromised.

MeSH Terms (22)

Animals Antibodies, Monoclonal Antibody-Dependent Cell Cytotoxicity Antibody Affinity Bacterial Proteins Binding Sites Breast Neoplasms Cell Membrane Female Humans Immunoglobulin Fragments Immunoglobulin G In Vitro Techniques Mice Mice, Inbred BALB C Mice, Inbred C57BL Peptide Hydrolases Rats Receptors, IgG Serine Endopeptidases Staphylococcus aureus Streptococcus pyogenes

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