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"Medical nanorobots can probably distinguish all of these cell types by surface chemical assay using chemosensor pads. Antigenic specificities exist for species (xenotype), organ, tissue or cell type for almost all cells possibly involving as many as 104 distinct antigens.

In the case of red blood cells, antigens in the Rh, Kell, Duffy, and Kidd blood group systems are found exclusively on the plasma membranes of erythrocytes and have not been detected on platelets, lymphocytes, granulocytes, in plasma, or in other body secretions such as saliva, milk, or amniotic fluid. Thus detection of any member of this four antigen set establishes a unique marker for red cell identification. MNSs and Lutheran antigens are also limited to erythrocytes with two exceptions: GPA glycoprotein (MN activity) also found on renal capillary endothelium, and Lublike glycoprotein which appears on kidney endothelial cells and liver hepatocytes. In contrast, ABH antigens are found on many nonRBC tissue cells such as kidney and salivary glands. In young embryos ABH can be found on all endothelial and epithelial cells except those of the central nervous system. ABH, Lewis, I and P blood group antigens are found on platelets and lymphocytes, at least in part due to adsorption from the plasma onto the cell membrane. Granulocytes have I antigen but no ABH.

ABO is the best known blood group system. Erythrocytes are typed as A, B, AB, or O, the latter indicating a lack of expression of either A or B. The H antigen is the precursor of A and B and is found on all red cell surfaces (up to ~1.7 x 106 antigens/RBC, or ~18,000/micron2) except those of patients with the rare Oh Bombay or H null phenotype. Because H is a precursor of A and B, type O erythrocytes have more H antigen than A or B erythrocytes, which in turn have more H antigen than AB erythrocytes (which express both A and B antigens). The number of A and B antigens on the red cell surface ranges from 12 x 106 (~10,00020,000/micron2); in 75% of Type A individuals, "double length" A antigens are also present (~500/micron2). MNSs factor antigens range from ~27005400/micron2, Rh factor antigens ~100300/micron2, Lewis factor antigens ~30/micron2, and so forth. Again assuming a ~(300 nm)2 chemotactic sensor pad, a nanorobot searching for a particular set of ~30 blood group antigens (Nspec = 30) requires t meas ~ 0.03 sec to make the self/nonself determination for a particular red cell membrane it has encountered. A nanorobot seeking to determine the complete blood group type of the membrane (e.g., in mapping mode) must in the worst case search all 254 known blood antigen types (Nspec = 254), requiring at most t meas ~ 2 sec.

Direct detection of blood group antigens, or of antibodies to blood group antigens in body fluids, permits at least partial self recognition by blood borne nanorobots without the need for any direct cell contact, which may be useful in establishing theater protocols. ABH, Lewis, I and P blood group antigens are found in blood plasma, and serum IgMclass antibodies associated with the carbohydrate antigens of the ABO, Lewis, and P blood group systems are almost universal. AntiM and antiN are common, antiSda is found in 12% of normal people, and antiVw or antiWra is found in ~1% of patients.960 In persons who previously have been pregnant or transfused, 0.160.56% have anti D (Rh group) and 0.140.60% have anti E and anti C (Rh system), anti K and anti Fya, and several other antibodies in serum. Body secretions contain ABH, I and Lewis antigen but no P system antigens; Sda antigen is found in most body secretions, with the greatest concentration in the urine.