Steinel Natalie C, Bolnick Daniel I
Department of Integrative Biology, The University of Texas at Austin, Austin, TX, United States.
Department of Medical Education, Dell Medical School, The University of Texas at Austin, Austin, TX, United States.
Front Immunol. 2017 Jul 17;8:827. doi: 10.3389/fimmu.2017.00827. eCollection 2017.
Melanomacrophage centers (MMCs) are aggregates of highly pigmented phagocytes found primarily in the head kidney and spleen, and occasionally the liver of many vertebrates. Preliminary histological analyses suggested that MMCs are structurally similar to the mammalian germinal center (GC), leading to the hypothesis that the MMC plays a role in the humoral adaptive immune response. For this reason, MMCs are frequently described in the literature as "primitive GCs" or the "evolutionary precursors" to the mammalian GC. However, we argue that this designation may be premature, having been pieced together from mainly descriptive studies in numerous distinct species. This review provides a comprehensive overview of the MMC literature, including a phylogenetic analysis of MMC distribution across vertebrate species. Here, we discuss the current understanding of the MMCs function in immunity and lingering questions. We suggest additional experiments needed to confirm that MMCs serve a GC-like role in fish immunity. Finally, we address the utility of the MMC as a broadly applicable histological indicator of the fish (as well as amphibian and reptilian) immune response in both laboratory and wild populations of both model and non-model vertebrates. We highlight the factors (sex, pollution exposure, stress, stocking density, etc.) that should be considered when using MMCs to study immunity in non-model vertebrates in wild populations.
黑素巨噬细胞中心（MMCs）是高度色素化吞噬细胞的聚集体，主要存在于许多脊椎动物的头肾和脾脏中，偶尔也见于肝脏。初步组织学分析表明，MMCs在结构上与哺乳动物生发中心（GC）相似，由此产生了MMCs在体液适应性免疫反应中起作用的假说。因此，MMCs在文献中常被描述为“原始GC”或哺乳动物GC的“进化前体”。然而，我们认为这种命名可能为时过早，因为它主要是从对众多不同物种的描述性研究中拼凑而来的。本综述全面概述了MMC的文献，包括对MMC在脊椎动物物种中分布的系统发育分析。在这里，我们讨论了目前对MMCs在免疫中的功能的理解以及尚存的问题。我们建议进行额外的实验，以证实MMCs在鱼类免疫中发挥类似GC的作用。最后，我们探讨了MMC作为鱼类（以及两栖类和爬行类）免疫反应的广泛适用的组织学指标在模型和非模型脊椎动物的实验室和野生种群中的效用。我们强调了在野生种群中使用MMCs研究非模型脊椎动物免疫时应考虑的因素（性别、污染暴露、应激、放养密度等）。
