High molecular weight Non-Immunoglobulin Salivary Agglutinins (NIA) bind C1q globular heads and have the potential to activate the first complement component

doi:10.1016/0161-5890(93)90059-K

Molecular Immunology

Volume 30, Issue 3, February 1993, Pages 309-319

https://doi.org/10.1016/0161-5890(93)90059-K Get rights and content

Abstract

Non-Immunoglobulin Salivary Agglutinins (NIA) which directly bind to microbes [including HIV] were studied for their potential to activate the first complement component (C1). It was determined that NIA had the same specific activity as heat aggregated IgG in binding to C1q and in activating C1.

In order to determine the region of Clq which bound to NIA, C1q globular heads and C1q stems (collagen-like regions) were prepared and separated via a Western blot procedure. NIA bound principally to the globular heads of C1q and weakly to the collagen-like stem region.

NIA were also studied for their potential to activate native C1 in normal human serum. Heat-aggregated IgG and cardiolipin served as positive controls. It was observed that incubation of isolated NIA with fresh normal human serum resulted in the formation of sodium dodecyl sulfate (SDS)-irreversible complexes of activated C1r-C1 inhibitor and activated C1s-C1 inhibitor and in activated C1s mediated C4 conversion. This indicated that isolated NIA had the potential to directly and effectively mediate classical complement pathway activation. Preincubation of NIA with C1q, blocked NIA mediated C1r and Cls activation and C4 conversion. The concn of NIA required to activate C1r and C1s was similar to that of heat-aggregated human IgG.

In kinetic ELISA, NIA or aggregated IgG (positive controls) were first immobilized on microtiter plates, blocked with gelatin then incubated with fresh human serum as a source of complement. Depositions of C4b, C3b and iC3b substantiated that the complement system was effectively activated by immobilized NIA. The optimal relative NaC1 concn for C4b deposition was 0.11 M.

While pre-incubation of NIA with C1q blocked the subsequent C1 fixing potential of NIA, pre-incubation of NIA with rgp160 [HIV-1] or fibronectin did not interfere with the potential of NIA to fix C1.

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When complement proteins enter the mucosa they may interact with endogenous molecules such as SALSA. SALSA binds directly to C1q, MBL and all three ficolins (Boackle et al., 1993; Gunput et al., 2015; Leito et al., 2011; Reichhardt et al., 2012). Surface-attached SALSA was shown to activate the complement system both through the interaction with C1q and MBL.
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The sample sizes of the other amyloidosis types are too small for statistical testing. DMBT1 has previously been demonstrated to be up-regulated in inflammatory conditions [25,26] and beyond that has been shown to interact with C1q of the complement cascade and to activate complement via the lectin pathway [19,20]. Cardiac amyloidosis is associated with inflammation in the surrounding tissue, raising the question as to whether this may be accompanied by a corresponding up-regulation of DMBT1 and complement factors.
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Both saliva and blood are carriers of antimicrobial factors such as SAG and complement respectively and it has been suggested that upon mixing with saliva, the complement system may contribute to host defense mechanisms within the oral cavity (Boackle, 1991). Early research by Boackle et al. (1993) demonstrated the potential of human SAG to bind C1q and to activate C1. The aim of the present study was to investigate the activation of complement by SAG in detail.
Salivary agglutinin (SAG), also known as gp-340 and Deleted in Malignant Brain Tumours 1, is a glycoprotein that is present in tears, lung fluid and mucosal surfaces along the gastrointestinal tract. It is encoded by the Deleted in Malignant Brain Tumours 1 gene, a member of the Scavenger Receptor Cysteine Rich group B protein superfamily. SAG aggregates bacteria thus promoting their clearance from the oral cavity and activates the complement system. Complement proteins may enter the oral cavity in case of serum leakage, which occurs after mucosal damage. The purpose of this study was to investigate the mode of complement activation. We showed a dose-dependent C4 deposition on SAG-coated microplates showing that either the classical or lectin pathway of complement was activated. Antibodies against mannose binding lectin inhibited C4 deposition and SAG induced no C4 deposition in MBL deficient sera showing SAG activated complement through the MBL pathway. Periodate treatment of SAG abolished MBL pathway activation consistent with an involvement of SAG glycans in complement activation. This provides the first evidence for a role of SAG in complement activation through the MBL pathway and suggests a potential role of SAG as a complement activating factor at the mucosal epithelia.
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Apoptotic cells are potent complement activators; and proposed mechanisms include IgM-mediated classical pathway activation, C-reactive protein (CRP)-mediated classical pathway activation, and IgM-mediated lectin pathway activation. While complement activation is beneficial in clearing apoptotic cells, the resulting complement-mediated inflammation may extend damage to the surrounding cells and tissues, as observed in ischemia/reperfusion injury. We previously engineered and characterized a single-chain Fv against C1q globular heads (scFv_QuVHVL) that blocked C1q binding to immobilized IgG and to IgG-sensitized cells, and thereby inhibited IgG-mediated classical pathway activation [Hwang H.Y., Duvall M.R., Tomlinson S., Boackle R.J., 2008. Highly specific inhibition of C1q globular-head binding to human IgG: a novel approach to control and regulate the classical complement pathway using an engineered single-chain antibody variable fragment. Molecular Immunology 45, 2570–2580].
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Molecular Immunology

Abstract

References (28)

The interactions of human complement with interfacially aggregated preparations of human secretory IgA

Immunochemistry

Saliva inhibits HIV-1 infectivity

J. Am. dent. Ass.

Salivary inhibition of HIV-1 infectivity: Functional properties and distribution in men, women and children

J. Am. dent. Ass.

Blockage of selected salivary mediated agglutination reactions by non-specific aggregated Fab fragments of IgG

The effects of aggregated IgG and IgG-immune complexes on the agglutination of bacteria mediated by non-immunoglobulin salivary agglutinins

Archs. Oral Biol.

Interaction of the envelope glycoprotein of human immunodeficiency virus with C1q and fibronectin under conditions present in human saliva

Molec. Immun.

In vitro inhibition of HIV-1 infectivity by human saliva

AIDS Res. and Human Retroviruses

The interaction of salivary secretions with the human complement system-A model for the study of host defense systems on inflamed mucosal surfaces

Crit. Rev. Oral Biol. Med.

An unusual complement-mediated hemolytic kinetics at low ionic strength

Molec. Immun.

Glycosaminoglycans enhance complement hemolytic efficiency. Theoretical considerations for GAG-complement-saliva interactions

Molec. Immun.

Characterization of C1 inhibitor binding to neutrophils

Immunology

Detection of functional complement components in gingival crevicular fluid from humans with periodontal disease

J. Dent. Res.

Salivary and amniotic-fluid agglutinin and aggregating factors: Evidence for complexing between high-molecular weight non-mucin glycoproteins and immunoglobulins

Biochem. Soc. Trans.

The nature of secretory agglutinins and aggregating factors. I: Secretory conglutinin-like factors, secretory bacterial aggregating factors and secretory IgA antibody in human saliva and amniotic fluid

Int. Arch. Allergy appl. Immun.

Cited by (52)

SARS-CoV-2 proteins regulate inflammatory, thrombotic and diabetic responses in human arterial fibroblasts

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A preliminary study of differentially expressed genes of the scallop Chlamys farreri against acute viral necrobiotic virus (AVNV)

Cardiac amyloidosis induces up-regulation of Deleted in Malignant Brain Tumors 1 (DMBT1)

The bacteria binding glycoprotein salivary agglutinin (SAG/gp340) activates complement via the lectin pathway

Specific inhibition of the classical complement pathway with an engineered single-chain Fv to C1q globular heads decreases complement activation by apoptotic cells