Evidence of the Presence of Rheumatoid Factor and Antibodies Reacting with Human and Rabbit IgA in Fluid from Non‐Keratinizing Jaw Cysts

Fluid from an apical periodontal and a follicular jaw cyst formed, in double diffusion in agarose gel, a continuous precipitin line against IgA isolated from human and rabbit serum, IgA myeloma protein, and secretory IgA. Results of immunoelectrophoresis and absorption experiments indicated that the IgA precipitating factor was an immunoglobulin belonging to the IgM class. Furthermore, the two cyst fluids contained immune complexes, possibly IgA‐anti‐IgA, which precipitated in agar gel. The same two cyst fluids showed a positive reaction in the Waaler‐Rose test with titres of 40 and 80, respectively. A series of other cyst fluids examined were negative in the Waaler‐Rose test. None of the cyst fluids contained antinuclear antibodies.