In the course of a study of the effects of formalin on red cells it was noted that formalin was capable of completely inhibiting the agglutinability of red cells by anti-sera without destroying the blood group antigens of the red cells.
At first, the effect of concentration of formalin and duration of treatment on the stability of red cells was examined. Various dilutions of formalin were made up in buffered saline, the solutions being adjusted to pH 7.3. Five per cent suspensions of washed human red cells were made with the diluted formalin and allowed to stand for varying lengths of time at 25°C.
The mixtures were centrifuged, and the formaimn treated red cells were washed 4 times with buffered saline.
It was observed that with short periods of standing in formalin there was some hemolysis on washing the treated red cells, but after 24 hours no hemolysis was observed upon washing the cells.
Agglutination tests were carried out by mixing dilutions of anti-sera with equal volumes of a 2per cent cell suspension, incubating at 37°C for 30 minutes, centrifuging the mixture and observing for agglutination by gently agitating the tubes.
The agglutinin titers observed with anti-A or anti-B sera and group A or group B red cells treated with various concentrations of formalin for 24 hours at 25°C are given in Table 1.
It is observed that the lower concentrations of formalin decrease the agglutinability of the red cells while the higher concentrations suppress it (Fig. 1).
Serum was absorbed by mixing one volume of washed packed cells with one volume of serum at room temperature for 15 minutes. The results of an absorption experiment with group A or group B red cells and anti-A or anti-B serum are given in Table 2.
It is observed that formalin-treated cells removed the agglutinin, while group B formalin treated cells did not remove the agglutinins from anti-A sera.
When the formalin treated red cells used in the absorption experiment were thoroughly washed, mixed with an equal volume of buffered saline and heated at 56°C. for 15 minutes, the specific agglutinin was eluted.