Cell-type specific surface markers

The hematopoietic lineage originally was worked out by Injecting the various types of precursor cells into mice whose precursor cells had been wiped out by irradiation. By observing which blood cells were restored in these transplant experiments, researchers could infer which precursors or terminally differentiated cells (e.g., erythrocytes, monocytes) arise from a particular type of precursor. The first step in these experiments was separation of the different types of hematopoietic precursors. This is possible because each type produces unique combinations of cell-surface proteins that can serve as type-specific markers. If bone marrow extracts are treated with fluorochrome-labeled antibodies for these markers, cells with different surface markers can be separated in a fluorescence-activated cell sorter (see Figure 5-34). 

The most obvious example of a cellular component of the immune system is the lymphocyte and includes all the various subtypes of T and B cells. As indicated previously, the fundamental distinction between T cells and B cells is based on the specific primary lymphoid organ in which the final stages of lymphopoiesis takes place. As described below, these cell types can also be distinguished based on their respective functions within the immune system as well as by phenotypic characteristics. For the purposes of this entry, a phenotype will be defined as a marker expressed on the surface of a cell which is genetically determined and which is frequently associated with the specific function of that... 

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