Importance of an increased gamma globulin level in the determination of Gm groups in collagen diseases.

Since it was demonstrated that some sera of rheumatoid arthritic patients would agglutinate human Rh-positive O-erythrocytes coated with a selected incomplete anti-Rh serum (Grubb, 1956; Waller and Vaughan, 1956), this phenomenon has been extensively investigated (for example, in Finland by Julkunen, Laine, Koskinen, and Tiilikainen, 1958). Grubb and Laurell (1956) showed that this agglutination is inhibited by some human sera. The inhibitory factor has been shown to belong to the gamma globulin fraction of the serum and to be a mendelian dominantly hereditary character. The corresponding phenotype is called Gm (a+), and its frequency in normal population lies between 55 and 95 per cent. (Grubb, 1959). 65 per cent. of a sample of 477 sera from the normal Finnish population were found to be Gm (a+) (MAkela and Tiilikainen, 1959), the corresponding recessive character Gm (a-) being found in the remaining 35 per cent.