Campos-Neto Antonio, Suffia Isabelle, Cavassani Karen A, Jen Shyian, Greeson Kay, Ovendale Pamela, Silva João S, Reed Steven G, Skeiky Yasir A W
Infectious Disease Research Institute, Seattle, Washington, USA.
Infect Immun. 2003 Sep;71(9):5065-76. doi: 10.1128/IAI.71.9.5065-5076.2003.
Several members of the Trypanosomatidae family, when freshly isolated from their mammalian hosts, have immunoglobulins adsorbed to their cell surfaces. However, a significant portion of these antibody molecules is not parasite specific, i.e., the immunoglobulins are bound to the parasite's cell surface molecules via noncognitive interactions. It has been proposed that this noncognitive adsorption of immunoglobulins to the parasite is mediated by an Fc-like receptor present in several members of the Trypanosomatidae family. However, the molecular identification of this receptor has never been defined. Here, we describe the cloning of a gene encoding a protein that might represent this molecule. The gene, named Lmsp1, was cloned by screening a Leishmania major cDNA expression library using a rabbit antiserum. Lmsp1 is present in both Leishmania and Trypanosoma and is expressed in all developmental stages of these parasites. The predicted protein has a molecular mass of 16.6 kDa and contains an RGD sequence starting at residue 104 and three cysteine residues at positions 55, 74, and 116. The purified recombinant protein strongly binds to normal immunoglobulins of various animal species (humans, rabbits, sheep, goats, guinea pigs, donkeys, rats, and mice) and the binding to human immunoglobulins appears to be immunoglobulin G (IgG) and IgM isotype specific. Moreover, Lmsp1 binds to both purified Fc and Fab fragments of IgG from both humans and rabbits. The mapping of the Lmsp1 epitopes that bind human IgG revealed that different sequences of the molecule bind to Fc or Fab. In addition, fluorescence-activated cell sorter analyses with a specific rabbit anti-Lmsp1 antiserum showed that Lmsp1 is associated with the parasite's cell surface. Finally, inhibition experiments point to an active role of this molecule in the immunoglobulin-mediated attachment and penetration of Trypanosoma cruzi in its macrophage host cells, thus suggesting that Lmsp1 is a putative Trypanosomatidae immunoglobulin receptor.
锥虫科的几个成员，当刚从其哺乳动物宿主中分离出来时，细胞表面吸附有免疫球蛋白。然而，这些抗体分子中有很大一部分并非寄生虫特异性的，即免疫球蛋白通过非特异性相互作用与寄生虫的细胞表面分子结合。有人提出，免疫球蛋白对寄生虫的这种非特异性吸附是由锥虫科几个成员中存在的一种类Fc受体介导的。然而，该受体的分子鉴定从未明确。在此，我们描述了一个可能代表该分子的蛋白质编码基因的克隆。该基因名为Lmsp1，通过用兔抗血清筛选硕大利什曼原虫cDNA表达文库进行克隆。Lmsp1存在于利什曼原虫和锥虫中，并在这些寄生虫的所有发育阶段表达。预测的蛋白质分子量为16.6 kDa，在第104位残基处有一个RGD序列，在第55、74和116位有三个半胱氨酸残基。纯化的重组蛋白能强烈结合各种动物物种（人类、兔子、绵羊、山羊、豚鼠、驴、大鼠和小鼠）的正常免疫球蛋白，并且与人类免疫球蛋白的结合似乎具有免疫球蛋白G（IgG）和IgM同种型特异性。此外，Lmsp1能结合来自人类和兔子的纯化IgG的Fc和Fab片段。对结合人类IgG的Lmsp1表位的定位显示，该分子的不同序列与Fc或Fab结合。此外，用特异性兔抗Lmsp1抗血清进行的荧光激活细胞分选分析表明，Lmsp1与寄生虫的细胞表面相关。最后，抑制实验表明该分子在克氏锥虫免疫球蛋白介导的附着和侵入其巨噬细胞宿主细胞过程中发挥积极作用，因此提示Lmsp1是一种假定的锥虫科免疫球蛋白受体。
