Isoagglutinin

These specific substances or blood group factors are detected by their property of inhibiting agglutinin reactions between human erythrocytes and heterologous human sera. This is the so-called isoagglutinin test which can detect the factors in dilutions of more than 1 part in 10 million. An even more sensitive but less specific test is their power to inhibit hemolysis of sheep s erythrocytes by the serum of rabbits immunized with certain human corpuscles. 

In connection with the apparent lack of correlation between precise chemical properties and blood group activity it is interesting to note that Witebsky and Klendshoj found no relationship between the reducing sugar contents of their preparations from human gastric juice and the isoagglutinin activity. 

In the other group, all the patients have been adults with a history of susceptibility to infection commencing between 19 and 29 years of age. These patients have presented with diarrhea, some evidence of malabsorption, and infestation with Giardia lamblia. Jejunal biopsy and radiology have revealed nodular lymphoid hyperplasia (H16). This syndrome is also seen with severe hypogammaglobulinemia in surviving adults (K4). Cases with isolated IgA deficiency where the absence of isoagglutinins has raised a suspicion of inadequate IgM are also described. 

The serum immunoglobulin pattern has been constant in these cases, and isoagglutinins were absent in four of the boys. The responses to oral poliomyelitis vaccine have been poor Since this oral vaccine usually evokes IgA antibodies, this suggests that the patients IgA may be largely inert. Subnormal responses to diphtheria and TAB are recorded. Lymphocyte transformation to PHA and delayed hypersensitivity were normal where tested. The tonsils, adenoids, thymus, and spleen were normal except in one case with lymphopenia, where tomography did not reveal any thymus, and tonsils, adenoids, and lymph nodes could not be detected (SI). The prognosis seems similar to that for Bruton s disease. 

This fraction contains virtually all the antibodies of plasma, as well as prothrombin, the isoagglutinins, plasminogen, and the component C, of complement. The separation of these various components is, of course, of major importance, and a systematic procedure has been developed by Oncley, Melin, Cameron, Richert and Gross (161). Briefly, it is based on the following observations ... 

The assay of isoagglutinin activity proved to raise considerable difficulties, for the techniques employed in different laboratories were so different in detail that the results were not quantitatively comparable, and the red cells used to observe the agglutination reaction inevitably varied somewhat from one individual donor to another. To eliminate these complications, Reference Standard preparations of anti-A and anti-B agglutinins were made up from certain preparations of Fraction III-l, and distributed to all investigators testing new preparations. By assay of the activity of a new preparation against the reference standard, studying both at a series of dilutions, the relative activity of different preparations could be reliably estimated (50). 

Just as Fraction III-2 consists of a few per cent of prothrombin, with a large amount of inert protein, so Fraction III-l consists only of about one per cent of isoagglutinins, the rest of the protein in this fraction not being directly involved in the reaction with A and B substances. Thus the properties of pure isoagglutinins cannot be deduced from those of the total protein in Fraction III-l but this fact does not impair the value of these preparations as blood t3rping reagents of high titer and avidity. 

Fraction II -f- III, obtained from the supernatant by precipitation with 25% ethanol by volume, at pH 6.8, r/2 = 0.09, temperature — 5 C., contains virtually all of the r-globulins (comprising the antibodies present), including both yi- and yi-globulins (69) prothrombin the isoagglutinins (anti-A, anti-B, anti-Rh) plas-... 

The method may be described briefly with the aid of a diagram. Plasma is adjusted to a pH of 7.2 addition of alcohol to a concentration of 8% precipitates fraction I, (mainly fibrinogen), which is centrifuged off. The supernatant is then brought to a pH of 6.9 and to an alcohol concentration of 25%. Precipitated fractions II and HI consist of p- and 7-globulins and contain all immunoproteins and blood-type specific isoagglutinins, in addition to part of the lipoproteins. 

Isoagglutinins are proteins which have an antibody-like specificity against foreign blood corpuscles, but which are present normally without the need to introduce an antigen artificially. Along with the blood-type substances of blood corpuscles, these isoagglutinins are responsible for the incompatibility in some blood transfusions (see Chapt. XVII-7). 

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