[Studies on the mechanism of L-agglutination (author's transl)]

The mechanism of L-agglutination (LA) was studied by fractionating human sera by means of Sephadex G 200 gel filtration. LA was found to be mediated by 2 factors: the rheumatoid factor (RF) as a macroglobulin, occuring only in sera from patients with rhematoid arthritis, and an IgG globulin, found also in normal sera, probably a highly prevalent incomplete streptococcal antibody. RF-containing IgM fractions, by themselves devoid of LA activity, can be rendered positive not only by IgG from the same serum, but also by IgG from normal sera or by commercial human IgG. After absorption of sera containing the RF with streptococci LA disappears; by addition of normal serum, IgG from normal serum or human IgG LA titers were attained similar to those of the respective native serum. A treatment of RF-containing sera with mercaptoethanol leads to a largely parallel disapperance of LA and latex fixation. Three substrains of Streptococcus pyogenes SF 130 (type) 1), Varying in their endowment with type-specific antigens, reacted similarly in LA.