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Kodama et al. (9) recently described a passive agglutination test using Toraysphere particles and made a comparative evaluation with conventional Ratz-Randall and NA-Latex-ASC (Hoechst) methods to measure anti-streptolysin O (ASO) titer for the diagnosis of group A streptococcal (GAS) infections such as pharyngitis and scarlet fever, and of rheumatic fever and glomerulonephritis as a consequence of GAS infection. The authors conclude that the agglutination test using Toraysphere particles is highly sensitive, specific, and convincing in determining ASO titer by binding of lipoprotein  to the particles. However, binding of other antigens, such as polysaccharide, protein, and DNA, to Toraysphere particles was not discussed.

In recent years, the use of (hem)agglutination assays has been limited or neglected, probably because of development of more sensitive techniques like enzyme-linked immunosorbent assays radioimmunoassays, and immunofluorescent assays. Simultaneously, the hemagglutination assay has interested some researchers with the availability of chemicals like diazotizing compounds or aldehydes to treat erythrocytes (5). Earlier studies have demonstrated the effects of treatment of erythrocytes with chemicals like tannic acid, resulting in aggregation by reducing the surface potential of erythrocytes (2) and aldehydes, making the cell surface anionic by elimination of free amino groups and rendering the cell more lipophilic. Their effects were thought to increase the affinity of the cells for protein through salt-like or nonionic forces (1, 4, 10). Treating erythrocytes with two aldehydes, creating double-aldehyde-stabilized (DAS) cells, offers several notable advantages over the existing passive hemagglutination (PHA) test, viz., (i) cells become nonsusceptible to lysis, (ii) cells can be stored at +4°C for long periods (10 to 12 months), (iii) cells have increased agglutination property, and (iv) aldehydes not only stabilize cells but also act as coupling agents by reacting with amino, sulfhydryl, and imidazole groups, rendering the cell more anionic and thus facilitating the firm attachment of antigens (3, 6). Experience of other workers has demonstrated the effective use of DAS cells, which greatly enhanced the sensitivity of PHA in the diagnosis of malaria (3), echinococcosis (11), leprosy (5), tuberculosis (6), and neurocysticercosis (8). In our experience, sensitized DAS cells had a long shelf life (14 to 16 weeks), prolonged stability, and retention of hemagglutinating potency if stored at +4°C (7). Thus, the merits of PHA if DAS cells are used as carrier particles are (i) the long shelf life of sensitized and unsensitized DAS cells; (ii) cost effectiveness; (iii) a high degree of sensitivity; (iv) no leaching of bound antigen from cells, as glutaraldehyde acts as both a coupling and a stabilizing agent; and (iv) a large number of samples can be assayed by microtitration. This method can be applied as a diagnostic and seroepidemiological tool since it has all the qualities which are needed for such a study.