Department of Biological Sciences, George Washington University, Washington, D.C., United States of America.
PLoS One. 2013 Aug 6;8(8):e70978. doi: 10.1371/journal.pone.0070978. Print 2013.
The cellular arm of the insect immune response is mediated by the activity of hemocytes. While hemocytes have been well-characterized morphologically and functionally in model insects, few studies have characterized the hemocytes of non-model insects. Further, the role of ontogeny in mediating immune response is not well understood in non-model invertebrate systems. The goals of the current study were to (1) determine the effects of caterpillar size (and age) on hemocyte density in naïve caterpillars and caterpillars challenged with non-pathogenic bacteria, and (2) characterize the hemocyte activity and diversity of cell types present in two forest caterpillars: Euclea delphinii and Lithacodes fasciola (Limacodidae). We found that although early and late instar (small and large size, respectively) naïve caterpillars had similar constitutive hemocyte densities in both species, late instar Lithacodes caterpillars injected with non-pathogenic E. coli produced more than a twofold greater density of hemocytes than those in early instars. We also found that both caterpillar species contained plasmatocytes, granulocytes and oenocytoids, all of which are found in other lepidopteran species, but lacked spherulocytes. Granulocytes and plasmatocytes were found to be strongly phagocytic in both species, but granulocytes exhibited a higher phagocytic activity than plasmatocytes. Our results strongly suggest that for at least one measure of immunological response, the production of hemocytes in response to infection, response magnitudes can increase over ontogeny. While the underlying raison d' être for this improvement remains unclear, these findings may be useful in explaining natural patterns of stage-dependent parasitism and pathogen infection.
昆虫免疫反应的细胞分支由血细胞的活性介导。虽然血细胞在模式昆虫中的形态和功能已经得到了很好的描述，但很少有研究描述非模式昆虫的血细胞。此外，在非模式无脊椎动物系统中，发育在调节免疫反应中的作用还不太清楚。本研究的目的是：(1)确定幼虫大小(和年龄)对未受挑战的幼虫和受非致病性细菌挑战的幼虫中血细胞密度的影响；(2)描述两种森林幼虫(Euclea delphinii 和 Lithacodes fasciola)中存在的血细胞活性和细胞类型多样性。我们发现，尽管早期和晚期幼虫(体型小和体型大，分别)在两种物种中的组成性血细胞密度相似，但晚期幼虫在注射非致病性大肠杆菌后产生的血细胞密度比早期幼虫高出两倍多。我们还发现，两种幼虫都含有浆血细胞、粒血细胞和嗜酸性血细胞，所有这些细胞都存在于其他鳞翅目昆虫中，但缺乏球形血细胞。在两种物种中，粒血细胞和浆血细胞都被发现具有强烈的吞噬作用，但粒血细胞的吞噬活性高于浆血细胞。我们的研究结果强烈表明，对于至少一种免疫反应的衡量标准，即对感染的血细胞反应，在发育过程中反应幅度可以增加。虽然这种改善的根本原因尚不清楚，但这些发现可能有助于解释阶段依赖性寄生和病原体感染的自然模式。
