Nossel H L, Butler V P, Wilner G D, Canfield R E, Harfenist E J
Thromb Haemost. 1976 Feb 29;35(1):101-9.
Distinction between fibrinopeptide A (FPA) and larger polypeptides containing the FPA sequence is critical for the interpretation of clinical results with FPA immunoassay methods. Therefore, the immunochemical reactivity of 14 rabbit anti-FPA sera with six different FPA containing antigens was studied in detail. Antigens tested included: fibrinogen; fragment E of fibrinogen; the amino-terminal disulfide knot of fibrinogen; Aalpha 1(Ala)-51(Met); Aalpha 1(Ala)-23(Arg); and, FPA. Synthetic partial sequences of FPA were also tested. The 14 FPA-specific antisera were divided into 3 distinct categories with: I, FPA immunoreactivity of larger polypeptides containing FPA approximately 1/100 of FPA on a molar basis, II, FPA immunoreactivity of the larger polypeptides intermediate between I and III; and III, FPA immunoreactivity of the larger polypeptides approximately equal to that of FPA on a molar basis. The antigenic determinants of a category I antiserum (R 2) are included in Aalpha 7(Asp)-16(Arg) with Asp(7), Phe(8) and Arg(16) being essential. When attached to FPA, the sequence Gly(17)-Arg(23) decreases the immunoreactivity of FPA with category I antisera 100-fold. The practical consequence of these findings is that, when category III antisera are employed, both FPA and larger FPA-containing polypeptides are equally immunoreactive. Since thrombin treatment of the larger polypeptides does not alter their immunoreactivity, category III antisera cannot discriminate between FPA and the larger polypeptides. On the other hand, with category I antisera, although the immunoreactivity of FPA itself is unaltered by thrombin treatment, larger polypeptides [e.g., Aalpha 1(Ala)-23tArg)] show a 100-fold increase in immunoreactivity following thrombin treatment and thus can readily be identified and separately quantitated. It is concluded that antisera with the specificity of category I are essential for the specific and accurate measurement of FPA, and for its distinction from larger FPA-containing polypeptides, in clinical plasma samples.
区分纤维蛋白肽A（FPA）与含有FPA序列的较大多肽对于用FPA免疫测定方法解释临床结果至关重要。因此，详细研究了14种兔抗FPA血清与6种不同含FPA抗原的免疫化学反应性。所测试的抗原包括：纤维蛋白原；纤维蛋白原E片段；纤维蛋白原的氨基末端二硫键结；Aα1（丙氨酸）-51（甲硫氨酸）；Aα1（丙氨酸）-23（精氨酸）；以及FPA。还测试了FPA的合成部分序列。14种FPA特异性抗血清分为3个不同类别：I类，含FPA的较大多肽的FPA免疫反应性在摩尔基础上约为FPA的1/100；II类，较大多肽的FPA免疫反应性介于I类和III类之间；III类，较大多肽的FPA免疫反应性在摩尔基础上与FPA大致相等。I类抗血清（R 2）的抗原决定簇包含在Aα7（天冬氨酸）-16（精氨酸）中，其中天冬氨酸（7）、苯丙氨酸（8）和精氨酸（16）是必需的。当与FPA连接时，序列甘氨酸（17）-精氨酸（23）使FPA与I类抗血清的免疫反应性降低100倍。这些发现的实际结果是，当使用III类抗血清时，FPA和含FPA的较大多肽具有同等的免疫反应性。由于对较大多肽进行凝血酶处理不会改变其免疫反应性，III类抗血清无法区分FPA和较大多肽。另一方面，对于I类抗血清，尽管FPA本身的免疫反应性不受凝血酶处理的影响，但较大多肽[例如，Aα1（丙氨酸）-23（精氨酸）]在凝血酶处理后免疫反应性增加100倍，因此可以很容易地被识别并单独定量。得出结论，具有I类特异性的抗血清对于在临床血浆样本中特异性和准确地测量FPA以及将其与含FPA的较大多肽区分开来至关重要。
