Pathogenic microorganisms employ numerous molecular strategies in order to delay or circumvent recognition by the immune system of their host. One of the most widely used strategies of immune evasion is antigenic variation, in which immunogenic molecules expressed on the surface of a microorganism are continuously modified. As a consequence, the host is forced to constantly adapt its humoral immune response against this pathogen. An antigenic change thus provides the microorganism with an opportunity to persist and/or replicate within the host (population) for an extended period of time or to effectively infect a previously infected host. In most cases, antigenic variation is caused by genetic processes that lead to the modification of the amino acid sequence of a particular antigen or to alterations in the expression of biosynthesis genes that induce changes in the expression of a variant antigen. Here, we will review antigenic variation systems that rely on homologous DNA recombination and that are found in a wide range of cellular, human pathogens, including bacteria (such as Neisseria spp., Borrelia spp., Treponema pallidum, and Mycoplasma spp.), fungi (such as Pneumocystis carinii) and parasites (such as the African trypanosome Trypanosoma brucei). Specifically, the various DNA recombination-based antigenic variation systems will be discussed with a focus on the employed mechanisms of recombination, the DNA substrates, and the enzymatic machinery involved.

中文翻译：

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由同源 DNA 重组介导的微生物抗原变异。

病原微生物采用多种分子策略来延迟或规避宿主免疫系统的识别。最广泛使用的免疫逃避策略之一是抗原变异，其中微生物表面表达的免疫原性分子被不断修饰。因此，宿主被迫不断调整其体液免疫反应来对抗这种病原体。因此，抗原性变化为微生物提供了在宿主（群体）内持续和/或复制较长时间或有效感染先前感染的宿主的机会。在大多数情况下，抗原变异是由遗传过程引起的，遗传过程导致特定抗原的氨基酸序列的修饰或导致变异抗原表达变化的生物合成基因表达的改变。在这里，我们将回顾依赖同源 DNA 重组的抗原变异系统，这些系统存在于多种细胞、人类病原体中，包括细菌（如奈瑟菌属、疏螺旋体属、梅毒螺旋体和支原体属），真菌（如卡氏肺囊虫）和寄生虫（如非洲锥虫布氏锥虫）。具体来说，将讨论各种基于 DNA 重组的抗原变异系统，重点是所采用的重组机制、DNA 底物和所涉及的酶机制。