Department of Medicine, Division of Allergy and Infectious Diseases, University of Washington, Seattle, Washington, USA.
Department of Medicine, Division of Allergy and Infectious Diseases, University of Washington, Seattle, Washington, USA
Infect Immun. 2018 Mar 22;86(4). doi: 10.1128/IAI.00866-17. Print 2018 Apr.
Antigenic variation of the immunodominant MgpB and MgpC proteins has been suggested to be a mechanism of immune evasion of the human pathogen , a cause of several reproductive tract disease syndromes. Phase variation resulting in the loss of adherence has also been documented, but the molecular mechanisms underlying this process and its role in pathogenesis are still poorly understood. In this study, we isolated and characterized 40 spontaneous, nonadherent phase variants from -passaged cultures. In all cases, nonadherence was associated with the loss of MgpBC protein expression, attributable to sequence changes in the expression site. Phase variants were grouped into seven classes on the basis of the nature of the mutation. Consistent with the established role of RecA in phase variation, 31 (79.5%) variants arose via recombination with MgPa repeat regions that contain variable sequences. The remaining mutants arose via nonsense or frameshift mutations. As expected, revertants were obtained for phase variants that were predicted to be reversible but not for those that arose via an irreversible mechanism. Furthermore, phase variants were enriched in cultures exposed to antibodies reacting to the extracellular, conserved C terminus of MgpB but not in cultures exposed to antibodies reacting to an intracellular domain of MgpB or the cytoplasmic HU protein. Genetic characterization of the antibody-selected phase variants confirmed that they arose via reversible and irreversible recombination and point mutations within These phase variants resisted antibody-mediated growth inhibition, suggesting that phase variation promotes immune evasion.
免疫显性 MgpB 和 MgpC 蛋白的抗原变异被认为是人类病原体逃避免疫的一种机制，该病原体是多种生殖道疾病综合征的病因。已经记录到导致黏附丧失的相位变异，但该过程的分子机制及其在发病机制中的作用仍知之甚少。在这项研究中，我们从 -代培养物中分离和鉴定了 40 个自发的、非黏附的相位变体。在所有情况下，非黏附性都与 MgpBC 蛋白表达的丧失有关，这归因于表达部位的序列变化。根据突变的性质，相位变体分为七类。与 RecA 在相位变异中的既定作用一致，31（79.5%）个变体是通过与含有可变序列的 MgPa 重复区域的重组产生的。其余的突变体是由于无义或移码突变产生的。正如预期的那样，对于那些可预测为可逆的相位变体可以获得回复突变体，但对于那些通过不可逆机制产生的变体则不能。此外，在暴露于针对 MgpB 胞外保守 C 末端的抗体的 培养物中富集了相位变体，但在暴露于针对 MgpB 细胞内结构域或细胞质 HU 蛋白的抗体的培养物中则没有。针对抗体选择的相位变体的遗传特征分析证实，它们是通过可逆和不可逆重组以及 内的点突变产生的。这些相位变体抵抗抗体介导的生长抑制，表明相位变异促进了免疫逃避。
