Erbe D V, Pfefferkorn E R, Fanger M W
Department of Microbiology, Dartmouth Medical School, Hanover, NH 03756.
J Immunol. 1991 May 1;146(9):3145-51.
The three types of IgG FcR (Fc gamma RI, Fc gamma RII, Fc gamma RIII) on human leukocytes play an important role in elimination of antibody-coated infectious agents. To further understand the role of the different Fc gamma R in mediating this killing, we examined the ability of human myeloid and lymphoid cells to kill the protozoan Toxoplasma gondii in the presence of antitoxoplasma IgG or bispecific antibodies. Although human myeloid cells (monocytes, macrophages, neutrophils, and eosinophils) all lysed unsensitized T. gondii, killing by these cells was significantly enhanced by opsonization with antitoxoplasma rabbit IgG. Human lymphocytes, however, did not lyse T. gondii unless the parasites were coated with antibody. The role of antibody and Fc gamma R in mediating ADCC of T. gondii was then examined using bispecific antibodies made by chemically cross-linking Fab fragments of antitoxoplasma antibodies to Fab fragments of antibodies specific for human leukocyte surface Ag, including Fc gamma R. Thus, simultaneous binding of these bispecifics to parasites and effector cells allowed an evaluation of killing when T. gondii were targeted to each Ag independently. Bispecifics which targeted T. gondii to Fc gamma RI, II or III enhanced lysis by monocytes. However, similar results were obtained with bispecifics targeting T. gondii to non-Fc gamma R Ag (CD11b or beta 2-microglobulin) on monocytes. Likewise, polymorphonuclear leukocytes mediated significantly more lysis in the presence of bispecifics linking T. gondii to Fc gamma RII, Fc gamma RIII, or the two non-Fc gamma R Ag CD11b and beta 2-microglobulin. Thus, although human myeloid cells did not require antibody-Fc gamma R triggering to kill T. gondii, antibody appeared to enhance lysis by capturing and directing the parasites to the effector cell surface. Human lymphocytes, in contrast, mediated significant lysis of T. gondii only in the presence of bispecifics targeting T. gondii to Fc gamma RIII, indicating a requirement for specific triggering of Fc gamma RIII for killing by large granular lymphocytes. Consequently, using bispecifics to compare targeting to specific Ag, both non-Fc gamma R and Fc gamma R, allowed determination of the role of antibody-Fc gamma R interactions in T. gondii killing. In addition, these studies demonstrate the potential of bispecifics in determining the role of specific Ag in killing of or infection by pathogens.
人类白细胞上的三种IgG FcR（FcγRI、FcγRII、FcγRIII）在清除抗体包被的感染因子中发挥着重要作用。为了进一步了解不同FcγR在介导这种杀伤作用中的作用，我们检测了人类髓样细胞和淋巴细胞在抗弓形虫IgG或双特异性抗体存在的情况下杀伤原生动物弓形虫的能力。虽然人类髓样细胞（单核细胞、巨噬细胞、中性粒细胞和嗜酸性粒细胞）均可裂解未致敏的弓形虫，但抗弓形虫兔IgG的调理作用显著增强了这些细胞的杀伤能力。然而，人类淋巴细胞不会裂解弓形虫，除非寄生虫被抗体包被。随后，使用通过化学交联抗弓形虫抗体的Fab片段与针对人类白细胞表面抗原（包括FcγR）的抗体的Fab片段制备的双特异性抗体，研究了抗体和FcγR在介导弓形虫抗体依赖性细胞介导的细胞毒性（ADCC）中的作用。因此，这些双特异性抗体与寄生虫和效应细胞的同时结合，使得在弓形虫分别靶向每种抗原时能够评估杀伤作用。将弓形虫靶向FcγRI、II或III的双特异性抗体增强了单核细胞的裂解作用。然而，将弓形虫靶向单核细胞上非FcγR抗原（CD11b或β2-微球蛋白）的双特异性抗体也得到了类似结果。同样，在存在将弓形虫与FcγRII、FcγRIII或两种非FcγR抗原CD11b和β2-微球蛋白连接的双特异性抗体的情况下，多形核白细胞介导的裂解作用明显增强。因此，虽然人类髓样细胞杀伤弓形虫不需要抗体-FcγR触发，但抗体似乎通过捕获并将寄生虫引导至效应细胞表面来增强裂解作用。相比之下，人类淋巴细胞仅在存在将弓形虫靶向FcγRIII的双特异性抗体时才介导显著的弓形虫裂解，这表明大颗粒淋巴细胞杀伤需要FcγRIII的特异性触发。因此，使用双特异性抗体比较靶向特定抗原（包括非FcγR和FcγR）的情况，能够确定抗体-FcγR相互作用在弓形虫杀伤中的作用。此外，这些研究证明了双特异性抗体在确定特定抗原在病原体杀伤或感染中的作用方面的潜力。
