Antigen density cells

Flow Cytometric Analysis of Cell Surface Antigen Density... 

The third problem that needs to be controlled is that of spectral cross-over and the possibility of incorrect instrument compensation. As an example of a case in which controls for nonspecific staining, autofluorescence, and compensation are all critical, let us look at the staining of B lymphocytes for the CD5 marker present with only low density on their surface. As well as the problems created by nonspecific staining and by autofluorescence, the problem of spectral cross-over between fluorescein and phycoerythrin can particularly confuse the interpretation of results from this kind of experiment. Look at Figure 6.5. What we are interested in is the number of B lymphocytes that possess the CD5 surface antigen. These cells will appear in quadrant 2 of a contour plot of fluorescein fluorescence... 

Batch procedures can be useful as pre-flow enrichment of the cells of interest. They can also be used as alternatives to flow sorting if the cells of interest can be appropriately selected. Flow sorting, although slow, is generally the only alternative if multiple parameters are required to define the cells of interest, if antigen density on the cell surface is low, or if forward or side scattered light is part of the definition of the desired cells. 

D2. D Arena, G., Dell Olio, M., Musto, P., Cascavilla, N., Perla, G., Savino, L., and Greco, M. M., Morphologically typical and atypical B-cell chronic lymphocytic leukemias display a different pattern of surface antigenic density. Leuk. Lymphoma 42, 649-654 (2001). 

CD21 is a useful marker to identify neoplasms of follicular dendritic cells. The antigen density on dendritic reticulum cells is fairly high however, the same antigen is expressed at low levels on mantle zone B cells, which makes an excellent low-level control. 

CD56 (also known as neural cell adhesion molecule) is expressed on the cell surface of a number of different tissues including natural killer cells, glial and neurons. This antigen may be demonstrated on monocytic and myeloid leukemias, plasma cell dyscrasias, natural killer cell lesions, neural and astrocytic tumors as well as tumors with neuroendocrine differentiation. Antigen density on hematopoietic tumors tends to be at a lower level than on non-hematopoietic lesions and the validation with flow cytometry determination for this antigen is recommended. 

Good morphology of membranes and organelles + Proteins labeled in cells for 15 tim from the exposed surface + Demonstrated lower antigen density... 

One new approach that is being developed to enhance tumour specificity used monoclonal antibodies (mAb), raised against a particular type of tumour, as a kind of molecular "guided missile", with a porphyrin attached to the mAb as the light-activated "warhead." Tumour cells have different surface antigens to normal cells, and it is possible to raise mAbs specific for these antigens. Tumour cells also differ from normal cells in that they express a large number of low-density lipoprotein receptors. Hydrophobic photosensitisers may then be incorporated into a lipid moiety of such a receptor, and taken into the tumour cell via lysosomes. 

Hosokawa S, Tagawa T, Niki H et al (2003) Efficacy of immunoliposomes on cancer models in a cell-surface antigen-density-dependent manner. Br J Cancer 89 1545-1551... 

Quintana FJ, Gerber D, Kent SC, Cohen IR, Shai Y (2005) HIV-1 fusion peptide targets the TCR and inhibits antigen-specific T cell activation. J Chn Invest 115 2149-2158 Reeves JD, Gallo SA, Ahmad N, Miamidian JL, Harvey PE, Sharron M, Pohlmann S, Sfakianos JN, Derdeyn CA, Blumenthal R, Hunter E, Dorns RW (2002) Sensitivity of HIV-1 to entry inhibitors correlates with envelope/coreceptor affinity, receptor density, and fusion kinetics. Proc Natl Acad Sci USA 99 16249-16254... 

Inadequate performance may result from lack of antigen specificity, e.g., tumor-specific antigens are often differentiation antigens which also occur, although in a lower density on nontarget cells (Poste, 1984). 

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