Differential silver enhanced double labeling in immunoelectron microscopy

Improved immuno double labelling for cell and structural biology

Colloidal gold is the most widely used electron dense marker in biological electron microscopy. The development of procedures for making gold particles of very defined sizes has made double or even multiple labelling possible using gold of two or more different sizes. Lately a new type of electron dense marker has been developed consisting of ligand-stabilized metal atom clusters rather than colloidal particles. The differences between these two types of markers are highlighted and the advantages of using metal atom clusters for immuno labelling of certain biological specimens are discussed. Possible methods of distinguishing two such cluster labels in double labelling experiments are reviewed.

The determination of comparable labeling densities in quantitative immunoelectron microscopic double labeling studies

In quantitative ultrastructural studies using colloidal gold immunocytochemical techniques, labeling intensities vary according to the size of the probe used. Using postembedded indirect two-sided double labeling and single labeling protocols, the labeling characteristics of four antigens were studied using two probe sizes commonly used in double labeling studies. It was determined that the labeling intensity variation resulting from the use of different probe sizes was unpredictable after correcting for the increased probe size alone. It was possible, however, to obtain comparable labeling densities by first determining the labeling intensities for each probe size with its antigen in single label studies on serial sections and using the same procedure as the double labeling studies. A probe size correction factor for each antigen was calculated from these data. This factor was used to obtain comparable measurements of the relative abundance of each label.

Role of chondroitin sulfate glycosaminoglycans in mineralizing osteoblast-like cells: effects of hormonal manipulation

A monoclonal anti-chondroitin sulfate antibody (CS-56) that recognizes native chondroitin sulfate glycosaminoglycans (CSGAG) was used to quantify changes in CSGAG labeling levels in mineralizing human fetal osteoblast-like cell multilayers up to 40 days postconfluence. In control cultures, mean labeling of CSGAG increased in nonmineralized areas from around eight gold probes per micron 2 (gpm) at 20 days to 26 gpm at 40 days. Labeling was markedly increased in the mineralized tissue, to 560 gpm at 30 days and 580 gpm at 40 days. In beta-glycerophosphate-treated cultures, the mineralized areas were increased and appeared earlier (20 days) than in the control cultures. In these cultures, mean CSGASG labeling increased in nonmineralized areas from around 5 gpm at 20 days to 26 gpm at 30 days and was further increased in mineralized areas to 270 gpm at 20 days and 298 gpm at 30 days. Mineralization was not noted in cultures treated with 10(-8) M 1,25-dihydroxyvitamin D, and CSGAG labeling remained low (< 5 gpm) during the study period. These results indicate that an increase in immunoreactive CSGAG is associated with mineralization in this culture system. One possible interpretation of these findings is that proteoglycan molecules or at least their CSGAG side chains may be involved in the mineralization process.