Normal human serum has long been known to contain a high molecular weight protein component which is demonstrated by direct examination in the ultracentrifuge (1). This material, with a sedimentation constant of approximately 19 S, has been found in recent studies to be composed of two main types of protein, one migrating electrophoretically as an a2-globulin and the other as a ~,-globulin (2). The 19 S y-globulin is of particular interest because it appears to contain certain antibodies. Evidence has accumulated suggesting that some of the isoaggtutinins (1) and Wassermann antibodies (3), the complete Rh agglutinins (4), and certain pathological hemagglutinins (5) fall into this fraction. Chemical and immunologic differences between the 7 S and 19 S ~,-globulin indicate that the latter component is not a simple aggregate (6, 7).Molecules with an s rate greater than 19 S are not detectable in significant amounts in fresh normal serum observed directly in the ultracentrifuge. Thus far such proteins have been reported only in the sera of patients with WaldenstrSm's macroglobulinemia where they represent secondary components associated with marked elevation of the 19 S fraction (8).It is the purpose of this paper to describe a serum protein component with an s rate greater than 19 S in the y-globulin fraction of certain patients with rheumatoid arthritis, and to present preliminary data on its physical and chemical properties. Since sera from patients with rheumatoid arthritis are known to potentiate certain immunologic reactions such as the sensitized sheep cell agglutination, and form a precipitate with ~,-globulin, the relation of this component to these serologic reactions was investigated.
Materials and Methods
1.Ultracentrifugation.--Analytical examinations of whole sera and of isolated serum protein fractions were carried out in a Spinco model E ultracentrifuge. Results were quantitated according to methods described by Trautman (9). Although the initial observations were made on electrophoretically prepared "~,-globulin fractions, most of the subsequent studies were carried out on whole sera. This was preferable for purposes of quantitation because aggregation and selective loss of the high molecular weight fraction 425 on
In view of a high frequency of liver involvement in patients with essential mixed cryoglubulinemia, we looked for evidence for hepatitis B virus infection in 25 serum specimens and 19 cryoprecipitates obtained from 30 patients. Three of the 25 serum specimens contained Hbs Ag, and 12 had antibody. The frequency of positive results was increased to six and 11 of 19 respectively when cryoprecipitates were examined, and 14 of 19 (74 per cent) of the cryoprecipitates were positive for either HBs Ag or its antibody. Electron microscopy of four cryoprecipitates showed structures resembling the 20-nm and 27-nm spheres, tubules, as well as the Dane particles characteristic of hepatitis B virus infection. Since such infection appears to be involved in the pathogenesis of the syndrome, the term "essential mixed cryoglobulinemia" should be replaced by "mixed cryoglobulinemia secondary to hepatitis B virus" or perhaps to other viral infections.
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