Erythrocyte surface sialic acids. Compared with wt, surface sialic acids were about 22% reduced in tg6 erythrocytes (left) despite the fact that the population of the transgenic erythrocytes is younger. The polybrene agglutination test (right) confirmed these quantitative measurements. Many red cell clusters (arrowheads) could be observed with wt erythrocytes, whereas hardly any could be detected with tg6 erythrocytes. Original magnification 200 ×; means (± SD) of 4 independent experiments each.