Co-aggregation of micelle-like globules from human submandibular/sublingual and parotid saliva

Abstract

Salivary micelle-like globules (SMGs) closely related to the casein micelles in milk have been observed in human whole saliva (HWS) and in human parotid saliva (HPS). Isolation of the SMGs from HWS, by acidification to the iso-electric point, has been observed to result in markedly larger amounts of SMGs than for HPS. The hypotheses to be tested in the present study were that SMGs also exist in human submandibular/sublingual saliva (HSMSL) and that the SMGs, as present in the pure salivary secretions, are precursors of the whole saliva SMGs in the oral cavity. Stimulated HPS and HSMSL saliva were collected from five subjects and examined by TEM, zeta potential determinations, photon correlation spectroscopy (PCS) and bacterial agglutination studies. Mixing HSMSL saliva and HPS in the ratio 1:3 and analysis by TEM and PCS examined possible co-aggregation of SMGs from different sources. TEM studies of HSMSL saliva showed occasional SMG-like particles and many large particulate aggregates, while PCS analyses indicated structures varying in diameter from 100 to 600 nm (mean 340 nm). The zeta potential of HSMSL at physiological pH varied among subjects from −13 to −20 mV (mean −17 mV). HSMSL saliva and SMGs isolated from HSMSL saliva were able to agglutinate streptococcal strains. TEM studies of the saliva mixture showed many SMGs and a few large aggregates consisting of SMG-like structures with diameters in the range of 20–80 nm. PCS analyses indicated structures in the saliva mixture from 400 to 2000 nm in diameter (mean 1030 nm). The results of this study show that SMGs are also found in HSMSL and suggest that the SMGs in HWS are likely to be the result of a co-aggregation of SMGs from the pure salivary secretions.