Bouvet J P, Pirès R, Iscaki S, Pillot J
Institut Pasteur, Unité d'Immunologie Microbienne, Paris, France.
J Immunol. 1993 Sep 1;151(5):2562-71.
Protein Fv, a human sialoprotein recently described in the stools of patients suffering from liver diseases, binds the variable domain of H chains without impairing Ag binding. Normal subjects are shown here to secrete protein Fv under a hidden form, saturated with luminal Ig. In feces, the nonimmune complexes are essentially of 1800 and 800 kDa M(r); they contain protein Fv molecules bound with F(ab')2 fragments produced by cleavage of Secretory IgA during colonic transit. The 800-kDa complexes correspond to 6 molecules of F(ab')2 fragments bound to a sole protein Fv dimer. This was established by comparison with an in vitro-made complex having a valency of 6. Investigation of the role of protein Fv shows that in vitro addition of this free molecule to antivirus or to anti-Salmonella typhi antibodies allows or augments agglutination of the corresponding pathogens. This property is of major interest for secretory antibodies because it favors their role in Ag conveyance in the mucus stream. It seems therefore that protein Fv is a novel key factor of the immune defense in gut.
Fv蛋白是最近在肝病患者粪便中发现的一种人唾液蛋白，它能结合重链可变区而不影响抗原结合。本文显示，正常受试者以一种隐藏形式分泌Fv蛋白，该形式被腔内免疫球蛋白饱和。在粪便中，非免疫复合物的相对分子质量（M(r)）主要为1800和800 kDa；它们含有与结肠转运过程中分泌型IgA裂解产生的F(ab')2片段结合的Fv蛋白分子。800 kDa的复合物对应于6个F(ab')2片段分子与一个Fv蛋白二聚体结合。这是通过与体外制备的价态为6的复合物进行比较确定的。对Fv蛋白作用的研究表明，在体外将这种游离分子添加到抗病毒或抗伤寒沙门氏菌抗体中，可使相应病原体发生凝集或增强凝集作用。这一特性对于分泌性抗体非常重要，因为它有利于其在黏液流中输送抗原的作用。因此，Fv蛋白似乎是肠道免疫防御的一个新的关键因素。
