The reaction rate of glucose-6-phosphate dehydrogenase activity in liver sections from fed and starved rats has been monitored by the continuous measurement at 37 degrees C of the reaction product as it is formed using scanning and integrating microdensitometry. Control media lacked either substrate or both substrate and coenzyme. All reactions were nonlinear; however, subtraction of either of the controls from the test response produced linearity. Differing responses in sections of livers from fed and fasted rats indicate that the appropriate control medium for use in the assay of this dehydrogenase is one lacking both substrate and coenzyme rather than a medium containing coenzyme. The reaction rate was the same with each of the final acceptors. Problems with the diffusion of the formazan of BPST and with the failure to precipitate the formazan of Neotetrazolium make Tetranitro BT and Nitro BT the tetrazolium salts of choice in quantitative dehydrogenase assays.

We have investigated the effect of cytomegalovirus (CMV) infection on the expression of class I HLA antigens on fibroblasts in vitro. Scanning and integrating microdensitometry was used to quantitate the level of cytoplasmic class I antigen expression, and an antibody binding assay was used to quantitate cell surface expression of class I HLA molecules. CMV infection resulted in a significant increase in the level of cytoplasmic and cell surface class I HLA antigen expression of fibroblast monolayers. The maximal effect was seen at 72 hours postinfection and was observed with both the laboratory strain of CMV, strain AD169, and with CMV purified directly from clinical specimens. Part of the increased HLA expression was mediated by interferon released from infected cells; however, an additional direct effect of the virus itself has not been ruled out. Interferon-induced increased expression of class I HLA antigens was accompanied by increased binding of CMV to the cells, consistent with our recent demonstration that class I HLA molecules can function as a cellular receptor for CMV.

(4A0016) ductase as demonstrated immunocytochemically. BPST did not properly localize dehydrogenase activity, most probably because of the redistribution of formazan, due to its

The density of HLA-DR antigen expression on alveolar macrophages obtained by bronchoalveolar lavage from sarcoidosis patients and normal control subjects was quantified using scanning and integrating microdensitometry in conjunction with a monoclonal mouse anti-human HLA-DR antibody directly conjugated to fungal glucose oxidase. The density of HLA-DR antigen expression on alveolar macrophages was significantly increased in the pulmonary sarcoidosis patients compared with normal control subjects examined. The reproducibility, specificity and sensitivity establish the reliability and potential importance of this method of direct quantification of cell surface antigen expression. The demonstration of an increased density of Class II Major Histocompatibility Complex (MHC) antigen expression on alveolar macrophages in pulmonary sarcoidosis suggests that these cells may play a role in the induction of the immune responses at sites of disease activity in this poorly understood condition. Keywords HLA-DR antigen expression alveolar macrophages pulmonary sarcoidosis microdensitometry monoclonal antibody

Electrons, generated from dehydrogenase reactions, are transferred to oxygen in preference to neotetrazolium chloride. In model systems in solution the presence of a small amount of oxygen drastically reduces the rate of formazan production. The rate of reaction in tissue sections has been followed using scanning and integrating microdensitometry. As in solution, electrons are transferred preferentially to oxygen. However, oxygen seems unable to diffuse through the incubation medium and thus the supply of oxygen at the site of the enzyme activity becomes exhausted; the time taken to use up the oxygen will depend on the rate of the enzyme activity. It is only then that electrons are passed to the tetrazolium salt and formazan is precipitated.