Humoral immunity in root caries in an elderly population. I.

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Abstract
IgA, IgG and IgM antibody activity (ELISA Units/ml) to Streptococcus mutans, Actinomyces viscous and Escherichia coli CF8 in serum, parotid saliva and whole saliva was measured using the amplified ELISA (a‐ELISA) while the concentration (μg/ml) of each isotype of immunoglobulin as well as albumin and lactoferrin, was determined using sandwich ELISAs. Selection of suitable reagents from those commercially available was based on specificity tests using purified human immunoglobulin; most polyclonal reagents required further absorption to attain class specificity. Cross‐absorption studies indicated the absence of patient antibodies that were cross‐reactive among the bacteria studied, except for IgM in some cases. Expression of response in ELISA Units (E.U.) per μg of immunoglobulin, i.e. specific activity, revealed that IgG specific activity was significantly higher in parotid saliva than in either whole saliva or serum for all bacteria studied; serum and whole saliva did not differ except for the higher specific activity in whole saliva to E. coli. The value of one E.U. was determined using the Comparative Antibody‐immunoglobulin Capture Assay (CACA). Using this novel method, we estimated that about 0.05 percent of serum IgA was specific for Streptococcus mutans, 0.008 for Actinomyces viscosus and 0.004 for Escherichia coli CF8. The percentage of specific IgM antibodies was higher than for IgA and IgG. The concentration of IgA anti‐Streptococcus mutans, Actinomyces viscosus and Escherichia coli levels are approximately 92 ng/ml, 25 ng/ml and 16 ng/ml in whole saliva and 46 ng/ml, 9.4 ng/ml and 6.3 ng/ml in parotid saliva. We calculated that normal, elderly adults secrete circa 25 ng of IgA anti‐Streptococcus mutans per min into both whole and stimulated parotid saliva. The ratio of salivary antibodies to the locally produced protein, lactoferrin (LF) and the serum‐derived proteins (albumin) together with simultaneous monitoring of salivary flow rates, provide additional insight into saliva dynamics. Among randomly‐selected patients, IgA and LF concentrations are inversely correlated with flow rate and > 70% of the IgG in whole saliva can be calculated to be of local origin; the latter is also consistent with the higher specific activity of the IgG in whole saliva than in serum. Using albumin:IgG ratios, the small amount of IgG in parotid saliva can be accounted for by transudation from serum.

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