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Background: Storage of blood units (for 35-42 days, depending on the preservative solution) has been reported to induce changes (e.g., reduction of sialic acid level) in red cells that are expected to alter their aggregability., Study Design and Methods: The aggregability of stored red cells was monitored in their autologous plasma and compared to that obtained with washed cells in dextran-containing buffer throughout the storage period. Red cell aggregability was determined by using a computerized image analyzer of cell flow properties., Results: Blood storage induced changes in red cells that are associated with continuous increase of their aggregability. At the same time, blood storage was associated with a reduction in the level of plasma fibrinogen, the major aggregating agent in plasma. Accordingly, the increased red cell aggregability was observed in red cells stored in dextran-containing buffer, but not in red cells stored in autologous plasma., Conclusion: Because blood transfusion is routinely given to patients with normal or high fibrinogen level, the transfusion of stored red cells has the potential to induce increased aggregation in vivo, depending on the storage period. This should be taken into account when blood transfusion is considered, particularly for patients with microcirculatory disorders.

Th polyagglutinability is characterized by the agglutination of the red blood cells (RBC) by Arachis hypogaea, Medicago disciformis, Vicia cretica but, in contrast to the T phenomenon, not by Glycine max (Glycine soja). Because Th transformation of RBC has been obtained in vitro, the mechanism of Th polyagglutinability expression has been studied and reproduced experimentally. An enzyme with neuraminidase specificity has been isolated from the culture supernatant of Corynebacterium aquaticum, and further characterized (MW = 55,600 kDa, pH = 5.5, Km = 0.138 microM, Kcat = 0.22 micrograms). Reversely, Th transformation of RBC could be obtained by using other neuraminidases but in very mild conditions of hydrolysis. From our results, it can be concluded that by the release of less than 20 micrograms of sialic acid per 10(10) RBC, Th reactivity can be induced whereas hydrolysis of greater amounts of sialic acid (greater than 20 micrograms/10(10) RBC) give the classical T polyagglutinability.