目的　研究 Ａ 组β溶血性链球菌壁多糖的最具抗原性的部分，及与牛心瓣膜糖蛋白的交叉反应性。方法　设计了新的提取和纯化链球菌壁多糖抗原的技术—分子筛凝胶层析法，以双向琼脂免疫扩散法鉴定出最具抗原性的部分，并测定这部分多糖与牛心瓣膜糖蛋白交叉反应性。结果　发现 Ａ 组链球菌壁多糖由４ 部分组成，分子量分别为１５ ０００ 、３７ ０００ 、６６ ０００ 、１５０ ０００ 。其中最具抗原性的部分是３７ ０００ ，３７ ０００ 的多糖部分和牛心瓣膜糖蛋白能同时与风湿性心瓣膜炎的血清发生免疫反应。而病人血清中的抗体被瓣膜糖蛋白吸附后，则不再与细菌多糖反应。结论　 Ａ 组β溶血性链球菌壁多糖的最具抗原性的部分是３７ ０００ ，该部分与牛心瓣膜糖蛋白呈现交叉反应性。 Objective To study the most antigenic part of Group A hemolytic streptococcal wall polysaccharides and the cross-reactivity with bovine heart valve glycoprotein. Methods A new technique for extracting and purifying streptococcal wall polysaccharide antigens was designed and characterized by molecular sieve gel chromatography. The most antigenic part was identified by two-dimensional agar immunodiffusion, and this part of polysaccharide was determined to cross the bovine heart valve glycoprotein Reactivity. The results showed that streptococcus group A polysaccharide consists of four parts, the molecular weight of 15 000, 37 000, 66 000, 150 000 respectively. One of the most antigenic part is 37 000, 37 000 of the polysaccharide part and bovine heart valve glycoprotein at the same time with the rheumatic heart valve inflammation of the immune response. Antibodies in the patient’s serum are absorbed by the valve glycoprotein and no longer react with bacterial polysaccharides. Conclusion The most antigenic part of the group A β-hemolytic streptococcal wall polysaccharide is 37 000, which shows cross-reactivity with bovine heart valve glycoprotein.