Wilson M A, Kozel T R
Department of Microbiology, University of Nevada, Reno 89557.
Infect Immun. 1992 Mar;60(3):754-61. doi: 10.1128/iai.60.3.754-761.1992.
Encapsulated and nonencapsulated cryptococci differ in their activation of the complement system. Incubation of nonencapsulated cryptococci in normal human serum (NHS) initiates both the classical and alternative pathways. This activation is characterized by an immediate, synchronous activation and binding of C3 to the yeast cells. Encapsulated cryptococci activate only the alternative pathway. This activation is characterized by a delayed (4 to 5 min), asynchronous activation and binding of C3. We examined the properties of antibodies in NHS that mediate immediate, synchronous binding of C3 to nonencapsulated cryptococci and zymosan. Adsorption of NHS with nonencapsulated cryptococci or zymosan produced a 4- to 6-min delay in the kinetics for activation and binding of C3 from the adsorbed serum to each respective yeast cell. This delay was similar to the delay observed when nonencapsulated cryptococci or zymosan was incubated in NHS in which the classical pathway was blocked by chelation of Ca2+. Proteins bound to serum-treated nonencapsulated cryptococci or zymosan were eluted and found to be predominantly immunoglobulin G (IgG), with lesser amounts of IgM. The eluted IgG could restore to adsorbed serum the rapid early kinetics for activation and binding of C3 characteristic of classical pathway initiation. Cross-adsorption showed that there was considerable cross-reactivity between the antibodies which restored rapid, early activation kinetics to NHS adsorbed with zymosan or nonencapsulated cryptococci. Encapsulated cryptococci were unable to adsorb the antibodies from NHS that mediated the rapid, early activation and binding of C3 to zymosan and nonencapsulated cryptococci. The latter results show that occlusion of antigenic sites at the cryptococcal cell wall is a newly recognized property that can be added to the repertoire of biological activities of the cryptococcal capsule.
荚膜型和非荚膜型隐球菌在补体系统激活方面存在差异。将非荚膜型隐球菌置于正常人血清（NHS）中孵育会启动经典途径和替代途径。这种激活的特征是C3立即、同步激活并结合到酵母细胞上。荚膜型隐球菌仅激活替代途径。这种激活的特征是延迟（4至5分钟）、异步激活并结合C3。我们研究了NHS中介导C3立即、同步结合到非荚膜型隐球菌和酵母聚糖上的抗体特性。用非荚膜型隐球菌或酵母聚糖吸附NHS后，吸附血清中C3激活并结合到各自酵母细胞的动力学出现4至6分钟的延迟。这种延迟类似于当非荚膜型隐球菌或酵母聚糖在经典途径因Ca2+螯合而被阻断的NHS中孵育时观察到的延迟。与血清处理过的非荚膜型隐球菌或酵母聚糖结合的蛋白质被洗脱，发现主要是免疫球蛋白G（IgG），IgM含量较少。洗脱的IgG可以恢复吸附血清中经典途径起始时C3激活和结合的快速早期动力学特征。交叉吸附表明，恢复吸附了酵母聚糖或非荚膜型隐球菌的NHS快速早期激活动力学的抗体之间存在相当大的交叉反应性。荚膜型隐球菌无法从NHS中吸附介导C3快速、早期激活并结合到酵母聚糖和非荚膜型隐球菌上的抗体。后一结果表明，隐球菌细胞壁抗原位点的封闭是一种新认识到的特性，可被添加到隐球菌荚膜的生物活性库中。
