Cavill Dana, Waterman Sally A, Gordon Tom P
Flinders University of South Australia, Bedford Park, Australia.
Arthritis Rheum. 2003 Dec;48(12):3597-602. doi: 10.1002/art.11343.
Functional autoantibodies that inhibit M(3) muscarinic receptor (M3R)-mediated neurotransmission have been reported in patients with Sjögren's syndrome (SS) and in patients with scleroderma. Because of limited reports that intravenous immunoglobulin (IVIG) improves dysautonomia in primary SS, we investigated whether IVIG neutralizes the effect of anti-M3R antibodies on colon smooth muscle contractions, in an in vitro functional assay.
IgG obtained from patients with primary SS, patients with rheumatoid arthritis and secondary SS, and patients with scleroderma was tested, before and after coincubation with equimolar amounts of IVIG or its F(ab')(2) and Fc fractions, for the ability to inhibit carbachol-evoked colon smooth muscle contractions. In addition, patient IgG was passed through an IVIG F(ab')(2) column, and unretained IgG was tested for functional activity on colon smooth muscle strips. Purified IgG obtained from healthy adults was also examined for a neutralizing effect on anti-M3R antibody activity.
Inhibition of colon contractions was mediated by the Fab fraction of patient IgG. Coincubation of IgG from the 3 patient groups with IVIG or its F(ab')(2) fragment neutralized anti-M3R antibody-mediated inhibition of cholinergic smooth muscle contractions. Preabsorption of patient IgG with Sepharose-bound IVIG F(ab')(2) removed the anti-M3R inhibitory activity. In addition, purified IgG from each of 4 healthy adults neutralized the functional autoantibodies.
Anti-M3R antibody activity does not require receptor crosslinking. Antiidiotypic antibodies present in pooled IgG neutralize patient IgG-mediated inhibition of M3R cholinergic neurotransmission, providing a rationale for IVIG as a treatment of autonomic dysfunction in patients with SS and patients with scleroderma. Furthermore, antiidiotypic antibodies in healthy individuals may prevent the emergence of pathogenic anti-M3R autoantibodies.
在干燥综合征（SS）患者和硬皮病患者中已报道存在抑制M3毒蕈碱受体（M3R）介导的神经传递的功能性自身抗体。由于关于静脉注射免疫球蛋白（IVIG）改善原发性SS自主神经功能障碍的报道有限，我们在体外功能试验中研究了IVIG是否能中和抗M3R抗体对结肠平滑肌收缩的影响。
检测原发性SS患者、类风湿关节炎合并继发性SS患者以及硬皮病患者的IgG，在与等摩尔量的IVIG或其F(ab')(2)和Fc片段共同孵育前后，抑制卡巴胆碱诱发的结肠平滑肌收缩的能力。此外，将患者IgG通过IVIG F(ab')(2)柱，检测未保留的IgG对结肠平滑肌条的功能活性。还检测了从健康成年人获得的纯化IgG对抗M3R抗体活性的中和作用。
结肠收缩的抑制由患者IgG的Fab片段介导。3组患者的IgG与IVIG或其F(ab')(2)片段共同孵育可中和抗M3R抗体介导的胆碱能平滑肌收缩抑制。用与琼脂糖结合的IVIG F(ab')(2)对患者IgG进行预吸附可去除抗M3R抑制活性。此外，4名健康成年人每人的纯化IgG均可中和功能性自身抗体。
抗M3R抗体活性不需要受体交联。混合IgG中存在的抗独特型抗体可中和患者IgG介导的M3R胆碱能神经传递抑制，这为IVIG作为SS和硬皮病患者自主神经功能障碍的治疗提供了理论依据。此外，健康个体中的抗独特型抗体可能会阻止致病性抗M3R自身抗体的出现。
