Department of Immunology, Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20 C, SE10691 Stockholm, Sweden.
Vaccine. 2011 Dec 9;30(1):21-8. doi: 10.1016/j.vaccine.2011.10.063. Epub 2011 Nov 4.
The Plasmodium falciparum antigen 332 (Pf332), is a megadalton parasite protein expressed at the surface of infected red cells during later stages of the parasite's developmental cycle. Antibodies to different parts of this antigen have been shown to inhibit parasite growth and adherence to host cells with or without ancillary cells. However, the mechanisms involved in these inhibitions remain largely unknown. We further analysed the activities of specific antibodies with regard to their specific mechanisms of action. For these analyses, affinity purified human antibodies against epitopes in the C-terminal fragment of Pf332 (Pf332-C231) were employed. All purified antibodies recognized Pf332-C231 both by immunofluorescence and ELISA. IgG was the main antibody isotype detected, although all sera investigated had varying proportions of IgG and IgM content. All the antibodies showed a capacity to inhibit parasite growth in P. falciparum cultures to different extents, mainly by acting on the more mature parasite stages. Morphological analysis revealed the antibody effects to be characterized by the presence of a high proportion of abnormal schizonts (15-30%) and pyknotic parasites. There was also an apparent antibody effect on the red cell integrity, as many developing parasites (up to 10% of trophozoites and schizonts) were extracellular. In some cases, the infected red cells appeared to be disintegrating/fading, staining paler than surrounding infected and uninfected cells. Antigen reversal of inhibition confirmed that these inhibitions were antigen specific. Furthermore, the growth of parasites after 22-42h exposure to antibodies was investigated. Following the removal of antibody pressure, a decreased growth rate of these parasites was seen compared to that of control parasites. The present study confirms the potential of Pf332 as a target antigen for parasite neutralizing antibodies, and further indicates that epitopes within the C231 region of Pf332 should constitute important tools in the dissection of the role of Pf332 in the biology of the malaria parasite, as well as in the design of a malaria vaccine.
疟原虫蛋白 332（Pf332）是一种巨达尔顿的寄生虫蛋白，在寄生虫发育周期的后期表达于受感染的红细胞表面。针对该抗原不同部分的抗体已被证明可抑制寄生虫的生长和与宿主细胞的黏附，无论是否存在辅助细胞。然而，这些抑制作用的机制在很大程度上仍然未知。我们进一步分析了特定抗体的活性，以了解其特定的作用机制。为此，我们使用针对 Pf332 中 C 端片段（Pf332-C231）表位的亲和纯化人抗体进行了分析。所有纯化的抗体均通过免疫荧光和 ELISA 识别 Pf332-C231。检测到的 IgG 是主要的抗体同种型，尽管所有研究的血清都具有不同比例的 IgG 和 IgM 含量。所有抗体均显示出不同程度地抑制寄生虫在疟原虫培养物中的生长能力，主要作用于更成熟的寄生虫阶段。形态学分析表明，抗体的作用特征是存在大量异常裂殖体（15-30％）和固缩寄生虫。抗体对红细胞完整性也有明显的影响，因为许多发育中的寄生虫（多达 10％的滋养体和裂殖体）位于细胞外。在某些情况下，受感染的红细胞似乎正在解体/消失，比周围受感染和未感染的细胞更苍白。抗原逆转抑制证实了这些抑制是抗原特异性的。此外，还研究了抗体暴露 22-42 小时后寄生虫的生长情况。与对照寄生虫相比，去除抗体压力后，这些寄生虫的生长速度降低。本研究证实 Pf332 作为寄生虫中和抗体的靶抗原具有潜力，并且进一步表明 Pf332 的 C231 区域内的表位应构成Pf332 在疟原虫生物学中的作用以及疟疾疫苗设计中的重要工具。
