Classes of Markers

Pan-specific endothelial cell markers. This class of markers includes antigens, which are generically expressed on endothelial cells (e.g. CD31). 

The marker remains in the plasma without binding to proteins, and the filtrate is neither reabsorbed nor secreted by the renal tubule. Clearance rate of the marker from plasma equals the glomerular filtration rate (GFR). The polysaccharide, inulin, typifies this class of markers. 

Figure 1. Simplified flow chart of classes of biologic markers (indicated by boxes). Solid lines indicate progression, if it occurs to the next class of marker. Dashed lines indicate that individual susceptibility influences the rates of progression, as do other variables. Biologic markers represent a continuum of changes, and the classification of change might not always be distinct (adapted from Committee on Biological Markers of the National Research Council, USA, 1987)...

They cannot identify the type of bone or the location of the bone with the altered formation or resorption. In bone disorders in which bone resorption and formation are coupled and dramatically altered, either class of marker will identify changes in bone turnover. 

This class of lymphocytes differentiates from immuno-logically incompetent hematopoietic stem cells of the bone marrow within the thymus - hence, the name thymus-dependent (T-) lymphocytes. Two major subclasses develop simultaneously, T-helper lymphocytes (Th) and cytotoxic effector lymphocytes (Tc). The cytotoxic T-lymphocytes (carrying on the surface the differentiation marker CD8) destroy cells, which cany their cognate antigen bound to MHC class I molecules on the surface by inducing apoptosis. From an evolutionary point of view Tc cells appear to have developed predominantly to cope with vims infections. As vituses can only replicate within cells, Tc eliminate them by destroying their producers. 

Perhaps the oldest and most well-studied class of pharmacogenomic markers are the drug metabolizing enzymes. These include variants in genes which encode... 

This is not the only example. Recently, polymorphisms in the G protein p3-subunit gene have been shown to predict response to hydrochlorothiazide (Turner et al., 2001). Psaty et al. identified a subset of patients with a variant of the a-adducin gene that were associated with a lower risk of myocardial infarction and cerebral hemorrhage with diuretic therapy (Psaty et al., 2002). In addition, Genaissance has indicated that it has identified markers that predict the response to the statins, a class of drugs used to lower cholesterol. 

Tandem mass spectrometry (i.e., MS-MS) is another technique that has recently become popular for the direct analysis of individual molecular markers in complex organic mixtures [87,505,509,578 - 583]. This technique provides a rapid method for the direct analysis of specific classes of molecular markers in whole sample extracts. In this approach the system is set up to monitor the parent ions responsible for a specific daughter ion as described above and the distribution of parent ions obtained under these conditions should provide the same information as previously obtained by GC-MS [505, 582]. Even greater specificity can be achieved by a combination of GC-MS-MS [516,584]. In view of the complexity of COM samples and the need to detect the presence of individual organic compounds or classes of compounds, it would seem that MS-MS, especially coupled with GC, would be extremely valuable in future environmental organic geochemistry studies. 

Suppressor T cells were also shown to express a major histocompatibility complex (MHC) class II marker, I-J. However, because I-J was never cloned and its presence in the MHC never shown formally, there was considerable doubt as to the significance of I-J [reviewed in 3, 4]. 

Most contrast agents elicit nephrotoxicity because they are primarily excreted by the kidneys. However, when administered in small doses, they constitute a rich source of GFR markers. The two major classes of contrast agents that are finding clinical utility as GFR markers are iodinated aromatic compounds and metal complexes. lodinated aromatics such as iohexol and iothalamate (Fig. 13) are commonly used as contrast agents for computed tomography (GT). They also have pharmacokinetics similar to inulin and hence are useful indicators of renal status [215]. The iodinated molecules used for GFR measurements consist of a triiodo-benzene core and hydrophilic groups to enhance solubility in aqueous medium. 

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