The partial isolation and function of salivary factors which interact with the complement system: a possible role in mucosal immunity

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

When complement first contacts salivary secretions, as when gingival crevicular fluid first meets saliva at the gingival margin, complement function is enhanced. The immediate potentiation of the complement system at equal volume ratios of serum to saliva is due to several factors, including the lower ionic strength of saliva when compared with serum and the presence of certain salivary glyproteins such as the nonimmunoglobulin agglutinins that appear to simultaneously activate C1 and affect (sequester) certain complement control proteins, such as Factor H. This initial potentiation of the complement cascade by saliva may aid in defending the area immediately above the gingival crevice from oral microbiota that are being coated with a combination of serous exudate components and salivary components. As serum becomes much more diluted with saliva (i.e., crevicular fluid moves away from the supragingival area), the acidic proline-rich salivary proteins (APRP) begin to disrupt the unbound C1q-C1r2-C1s2 macromolecular complexes. Thus, the APRP along with other C1 fixing substances in saliva appear to restrict complement function, but only when the ratios of saliva to serum exceed 250:1. Since certain salivary glycoproteins bind to viruses, the potentiation of the complement system by saliva may also play a role in neutralizing certain viral infections on mucosal surfaces where tissue transudates containing complement begin to contact mucosal secretions such as saliva. Again, the ratio of serous fluid to mucosal secretion appears to be an important factor. This article also discusses some of our preliminary data and speculations concerning the binding of the self-associating high-molecular-weight nonimmunoglobulin salivary agglutinins (NIA) with the envelope of the human immunodeficiency virus (HIV) and the possible cooperative role of C1q and fibronectin in aiding neutralization of HIV infectivity.

Restriction of C1 hemolytic function by human proline-rich salivary proteins

Acidic proline-rich salivary proteins, PRPI, PRPII, PRPIII, PRPIV, upper Db and Statherin, were isolated from parotid saliva and tested for interaction with complement. It was determined that each of the isolated proline-rich proteins blocked C1 hemolytic activity in assay systems where C1 was rate-limiting. Further studies comparing the specific activity of the proline-rich proteins to unfractionated parotid saliva indicated that other salivary substances (sensitive to urea treatment of parotid saliva) were also interacting with the first complement component but in a time-dependent manner. Based on a series of experiments examining the effect of the sequence of addition of the proline-rich proteins in the complement assay systems, it is postulated that these salivary proteins are able to block the proper interaction of C1 with EAC4 cells (sheep erythrocytes coated with antibody and C4gp). The proline-rich salivary proteins had no effect on C1 once C1 was bound to the immune complexes on the EAC4 cells. The C1 macromolecular complex undergoes conformational changes upon interaction with immune complexes resulting in a more avid binding of the C1q-Clr-Cls subunits with one another. Thus it is speculated that the EAC4-bound C1 becomes resistant to disruption by the proline-rich salivary proteins. Although the urea-sensitive factors had the highest specific C1-fixing activity, the activity of the acidic proline-rich proteins on C1 is important because of their relatively high concern in salivary secretions. Since complement-containing serous exudates and transudates are present on inflamed mucosal tissues, salivary substances which interact with C1 may play a role in regulating the initiation of the classical complement pathway, particularly at those mucosal sites where there is a high ratio of salivary secretion to serous exudate.

In vitro alternative and classical activation of complement by extracts of cotton mill dust: a possible mechanism in the pathogenesis of byssinosis

Extracts of cotton mill dust (CDE) were shown to activate complement by the classical and alternative pathways. Activation of the classical pathway, presented in this study for the first time, was verified by C1 consumption, C2 destruction, and C4 conversion tests. The component of cotton dust that causes complement activation precipitated in the presence of 20% saturated ammonium sulfate. The data presented suggest that endotoxin is not the principal complement-activating component, as complement activation could not be correlated to endotoxin concentrations of extracts of various parts of the cotton plant. Proteolytic enzymes were also eliminated as possible causative agents of complement cleavage since CDE did not cleave purified C3 in the absence of other complement components. Polyvinylpolypyrrolidone failed to remove the complement-activating component in CDE demonstrating that polyphenolic tannins are not the causative agents. Involvement of complement activation in the pathogenesis of byssinosis could explain in part the mechanism and symptoms of the acute byssinotic reaction.

A postulated mechanism for heparin's potentiation of C1 inhibitor function

Conflicting reports exist in the literature concerning the primary mechanism for heparin's inhibition of C1 hemolytic function. We provide evidence here that heparin's most effective inhibition is mediated through interaction with and potentiation of C1-INH. The molecular nature of the interaction between heparin and the C1-INH molecule is evidenced by an anodal shift in the electrophoretic mobility of C1-INH upon the addition of heparin.l We also demonstrate that C3 and C4 conversions in normal human serum by classical pathway activators such as heat-aggregated IgG are inhibited by addition of heparin, yet heparin does not prevent similar C3 conversion in serum depleted of C1-INH Heparin's inhibitory action is restored to C1-INH-depleted serum by the addition of purified C1-INH.

Disruption of complement-mediated reactions by insoluble dentifrice ingredients

It has been strongly suggested that the complement system plays a critical role in the pathological processes occurring in periodontal disease. Because individuals with this common disease are often instructed to brush their teeth more often and for longer periods of time, several commercial toothpastes were tested for their effects on complement-mediated reactions. In this study, six of the nine toothpastes tested activated the classical complement pathway, leading to C3 cleavage, as determined by crossed immunoelectrophoresis. The activating ingredients were contained in the insoluble fraction of the toothpastes. Of the toothpaste abrasives, Ca++ pyrophosphate was determined to have C3-converting activity. One of the toothpastes, which contains a particular type of amorphous silica abrasive, appeared to bind both native C3 and its conversion products. In general, disruption of complement-mediated functions in affected tissues could alter local immunological responses and interfere with healing. The in vitro studies described here suggest a need for clinical studies to ascertain the in vivo influences of dentifrice ingredients on complement-mediated reactions in periodontal disease.