The relationship between natural and immune haemolysins and incompatibility of 51Cr labelled red cells in the sheep.

The use of Cr as a label for sheep red cells was tested in thirteen sheep in which small volumes of labelled cells were injected. A considerable loss of radioactivity from the circulating blood was noted especially during the first few days, which seemed to be due to the elution of chromium from the cells. This was supported by certain experiments. The method, however, offered a practical possibility for determining the incompatibility of homologous red cells. The strength of the naturally occurring antibodies was determined by an haemolytic test. These antibodies were associated with an elimination of the appropriate injected cell, the rate depending upon the strength of the antibody. The method should prove useful in selecting bloods for transfusion. The rate of elimination of injected cells was followed before and after immunization. In most cases the elimination was virtually complete, but examples have been met with in which a proportion of the cells remained circulating in the presence of antibody.