IgG Proteolytic Activity of Pseudomonas aeruginosa in Cystic Fibrosis

Abstract

To study how fragmented IgG antibodies might arise within the respiratory secretions of individuals with cystic fibrosis (CF), we screened protease extracts from CF polymorphonuclear leukocytes and mucoid and nonmucoid transformants of Pseudomonas aeruginosa from patients with CF for IgG proteolytic activity. All strains of P. aeruginosa tested exhibited IgG proteolytic activity. Incubation for 7 hr at 37 C was required to demonstrate generation of free Fc gamma immunoreactivity. Further analysis of these cleavage products of CF IgG demonstrated generation of Fc gamma polypeptides with 4S sedimentation coefficients and F(ab')2 fragments with 5S coefficients. Bacterial IgG proteolytic activity was inhibited by EDTA and was associated with levels of bacterial elastase exceeding 5 micrograms/mg of total protein. Pseudomonas elastase was significantly more active on IgG1 and IgG3; IgG2 and IgG4 were more resistant. This bacterial exoproduct appears to digest IgG molecules into Fab gamma, F(ab')2 fragments, and a free Fc gamma piece with a molecular weight of 40,000.

Altered Antibody Isotype in Cystic Fibrosis. Possible Role in Opsonic Deficiency

“…This hypothesis is supported by experiments showing degradation of IgG by PA elastase in vitro (13,14) and fragmentation of PA LPS IgG antibody from bronchial lavage fluid of CF patients in vivo (1 1).…”

Cleavage of IgGs by proteases associated with invasive diseases

“…[38][39][40] Also, a number of microorganisms express immunoglobulin-degrading proteases that have been implicated as virulence factors in aiding bacterial colonization. 8,41,42 Other examples of bacterial IgG-degrading proteases include Streptococcal SpeB that cleaves IgG in the upper hinge, 43,44 a Pseudomonas elastaselike enzyme, 45 Mirabilysin of Proteus mirabilis, 46 and Trepolisin of Treponema denticola.…”

“…9 Indeed, only limited data exist for the presence of IgG breakdown products in biological samples and those were primarily limited to severely inflammatory settings and focused on Fab and F(ab') 2 products. [57][58][59] It can only be speculated whether localized secretion of IgGdegrading proteases represents a mechanism to quell the inherent inflammatory potential of antibodies. We and others have had our attention drawn to the group of proteases that are expressed by invasive and pathological cells, e.g., tumor cells and bacteria, although enzymes from non-pathological sources, e.g., neutrophil elastase and other human extracellular proteases, might also contribute to IgG breakdown.…”

Human Anti-IgG1 Hinge Autoantibodies Reconstitute the Effector Functions of Proteolytically Inactivated IgGs

“…However, our group and others have shown that several proteases secreted or expressed in environments where Igs are present can cleave Igs in the hinge region, resulting in a number of cleavage products, including Fab or F(abЈ) 2 (1)(2)(3). These fragments retain the ability to bind to their respective epitopes but lose Fcmediated effector functions that are dependent on Fc domain interactions with Fc receptors, complement, etc.…”

“…The matrix metalloproteinases (MMPs) 3 matrilysin (MMP-7) and stromelysin-1 (MMP-3) were reported to cleave all subclasses of human IgG in a step-wise process (4). Certain bacterial proteases have been shown to possess strict selectivity for mammalian IgGs (8 -10) The IgG-degrading enzyme of Streptococcus pyogenes (IdeS) specifically cleaves human IgG1 between glycine 236 and glycine 237 (EU numbering) (11) in the lower hinge (1,9,12).…”