Tsuboi Hiroto, Matsuo Naomi, Iizuka Mana, Nakamura Yumi, Matsumoto Isao, Sumida Takayuki
Division of Clinical Immunology, Doctoral Program in Clinical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba.
Nihon Rinsho Meneki Gakkai Kaishi. 2010;33(4):222-8. doi: 10.2177/jsci.33.222.
Sjögren's syndrome (SS) is an autoimmune disease that affects exocrine glands including salivary and lacrimal glands. It is characterized by lymphocytic infiltration into exocrine glands, leading to dry mouth and eyes. A number of auto-antibodies, such as anti-SS-A and SS-B antibodies, are detected in patients with SS. However, no SS-specific pathologic auto-antibodies have yet been found in this condition. M3 muscarinic acetylcholine receptor (M3R) plays a crucial role in the secretion of saliva from salivary glands. It is reported that some patients with SS carried inhibitory auto-antibodies against M3R. To clarify the epitopes and function of anti-M3R antibodies in SS, we examined antibodies to the extracellular domains (N terminal region, the first, second, and third extracellular loop) of M3R by ELISA using synthesized peptide antigens encoding these domains in 42 SS and 42 healthy controls (HC). Titers and positivity of anti-M3R antibodies to every extracellular domain of M3R were significantly higher in SS than in HC. For functional analysis, human salivary gland (HSG) cells were pre-cultured with IgG from anti-M3R antibodies positive SS, negative SS, and HC. HSG cells were stimulated with cevimeline hydrochloride and intracellular calcium concentration (Ca(2+)) was measured. IgG from anti-M3R antibodies to the second loop positive SS inhibited the increase of Ca(2+), but IgG from antibodies to the N terminal or the first loop positive SS enhanced it, while IgG from antibodies to the third loop positive SS showed no effect on Ca(2+) as well as IgG from anti-M3R antibodies negative SS and HC. These findings indicated the presence of several B cell epitopes on M3R in SS and effect of anti-M3R antibodies on the salivary secretion might differ with these epitopes.
干燥综合征（SS）是一种自身免疫性疾病，会影响包括唾液腺和泪腺在内的外分泌腺。其特征是淋巴细胞浸润外分泌腺，导致口干和眼干。SS患者体内可检测到多种自身抗体，如抗SS - A和SS - B抗体。然而，在这种疾病中尚未发现SS特异性的病理性自身抗体。M3毒蕈碱型乙酰胆碱受体（M3R）在唾液腺分泌唾液过程中起关键作用。据报道，一些SS患者携带针对M3R的抑制性自身抗体。为了阐明SS中抗M3R抗体的表位和功能，我们使用编码这些结构域的合成肽抗原，通过酶联免疫吸附测定（ELISA）检测了42例SS患者和42例健康对照（HC）针对M3R细胞外结构域（N端区域、第一、第二和第三细胞外环）的抗体。SS患者中针对M3R每个细胞外结构域的抗M3R抗体滴度和阳性率均显著高于HC。为进行功能分析，将来自抗M3R抗体阳性的SS、抗M3R抗体阴性的SS以及HC的IgG与人类唾液腺（HSG）细胞预培养。用盐酸西维美林刺激HSG细胞并测量细胞内钙浓度（Ca(2 +)）。来自第二环抗M3R抗体阳性的SS的IgG抑制了Ca(2 +)的升高，但来自N端或第一环抗M3R抗体阳性的SS的IgG增强了Ca(2 +)，而来自第三环抗M3R抗体阳性的SS的IgG对Ca(2 +)无影响，抗M3R抗体阴性的SS和HC的IgG也无影响。这些发现表明SS中M3R上存在多个B细胞表位，且抗M3R抗体对唾液分泌的影响可能因这些表位而异。
