Moore T L, Dorner R W, Weiss T D, Baldassare A R, Zuckner J
Arthritis Rheum. 1981 Oct;24(10):1283-90. doi: 10.1002/art.1780241008.
Hidden 19S IgM rheumatoid factors (RF)-i.e., RF detected in the IgM-containing fraction after separation of the serum at an acid pH-have been found in 68% of patients with seronegative juvenile rheumatoid arthritis (JRA). Inhibition studies utilizing a hemolytic assay for RF were performed to determine the specificity of hidden 19S IgM RF. Sera from 14 children with JRA were separated by gel filtration at pH 4.05. Two were seropositive for RF and 12 were seronegative; the latter had high titer hidden 19S IgM RF. The IgM-containing fractions were preincubated with monomeric human IgG, rabbit IgG, or bovine IgG, and the complement-dependent hemolytic assay ws performed. The RF in the IgM fraction from the 2 seropositive patients were inhibited most strongly by rabbit IgG, whereas hidden RF in the IgM fraction of 9 seronegative patients were inhibited markedly by human IgG (homologous IgG equal to autologous IgG), poorly by rabbit IgG, and not at all by bovine IgG. Further inhibition studies with the hidden 19S IgM RF demonstrated inhibition by the human IgG1 subclass in all patients and only minimal inhibition by the IgG3 subclass in 3 patients. Inhibition with IgG1 Fc fragments produced by papain and thermolysin digestion demonstrated inhibition by only those fragments that contained the G1m (a) antigenic area which is found in the C gamma 3 homology area of the IgG1 molecule. These data indicate that hidden 19S IgM RF possibly circulate as immune complexes bound to the IgG1 molecule and the binding chiefly occurs in th G1m (a) homology area.
隐匿性19S IgM类风湿因子（RF）——即在酸性pH值下分离血清后在含IgM组分中检测到的RF——在68%的血清阴性幼年类风湿性关节炎（JRA）患者中被发现。利用RF溶血试验进行抑制研究以确定隐匿性19S IgM RF的特异性。14例JRA患儿的血清在pH 4.05下通过凝胶过滤进行分离。2例RF血清学阳性，12例血清学阴性；后者具有高滴度隐匿性19S IgM RF。将含IgM的组分与单体人IgG、兔IgG或牛IgG预孵育，然后进行补体依赖性溶血试验。2例血清学阳性患者IgM组分中的RF被兔IgG抑制最强，而9例血清学阴性患者IgM组分中的隐匿性RF被人IgG（同源IgG等同于自身IgG）显著抑制，被兔IgG抑制较弱，且完全不被牛IgG抑制。对隐匿性19S IgM RF的进一步抑制研究表明，所有患者中均被人IgG1亚类抑制，3例患者中仅被IgG3亚类轻微抑制。用木瓜蛋白酶和嗜热菌蛋白酶消化产生的IgG1 Fc片段进行抑制试验表明，只有那些含有在IgG1分子Cγ3同源区发现的G1m（a）抗原区的片段才有抑制作用。这些数据表明，隐匿性19S IgM RF可能以与IgG1分子结合的免疫复合物形式循环，且结合主要发生在G1m（a）同源区。
