Johns R, Ohnishi J, Broadwater A, Sonenshine D E, De Silva A M, Hynes W L
Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA.
J Med Entomol. 2001 Jan;38(1):99-107. doi: 10.1603/0022-2585-38.1.99.
The blacklegged tick, Ixodes scapularis Say, transmits the Lyme disease spirochete Borrelia burgdorferi, whereas the American dog tick, Dermacentor variabilis (Say), is unable to transmit the bacterium. We compared the innate immune response of these ticks against spirochetes directly inoculated into the hemocoel cavity of ticks. In I. scapularis, some Borrelia were found associated with hemocytes, while numerous other spiral-shaped, intact bacteria remained free in the hemolymph. In contrast, in D. variabilis only remnants of the bacteria were evident in the hemolymph, indicating lysis; intact spirochetes were rare. Spirochetes were observed bound to or within the organs of both tick species, although many more spirochetes were found associated with the I. scapularis organs. The few spirochetes observed with the D. variabilis organs appeared to be dead because D. variabilis tissues rarely contained culturable bacteria, unlike I. scapularis tissues. When spirochetes were incubated with I. scapularis hemolymph plasma in vitro, bacterial survival and motility were not reduced. In contrast, incubation of spirochetes with D. variabilis hemolymph plasma resulted in > 50% of the spirochetes becoming nonmotile by 45 min. The differences in the responses of the two different tick species indicate that I. scapularis is immunotolerant when challenged with B. burgdorferi and dependent on a slow phagocytic response to clear Borrelia from the hemolymph. In contrast, D. variabilis is highly immunocompetent (i.e., innate immunity), using plasma borreliacidal factors and a rapid increase in phagocytic cells to clear the infection and limit tissue invasion.
黑腿蜱（肩突硬蜱，Ixodes scapularis Say）传播莱姆病螺旋体伯氏疏螺旋体（Borrelia burgdorferi），而美洲犬蜱（变异革蜱，Dermacentor variabilis (Say)）则无法传播该细菌。我们比较了这两种蜱对直接接种到蜱血腔中的螺旋体的先天免疫反应。在肩突硬蜱中，发现一些伯氏疏螺旋体与血细胞相关，而许多其他螺旋形的完整细菌仍游离于血淋巴中。相比之下，在变异革蜱的血淋巴中仅可见细菌残骸，表明细菌已裂解；完整的螺旋体很少见。在两种蜱的器官中均观察到螺旋体附着于器官表面或在器官内部，尽管与肩突硬蜱器官相关的螺旋体数量更多。在变异革蜱器官中观察到的少数螺旋体似乎已死亡，因为与肩突硬蜱组织不同，变异革蜱组织中很少含有可培养的细菌。当螺旋体在体外与肩突硬蜱血淋巴血浆孵育时，细菌的存活和运动能力并未降低。相比之下，螺旋体与变异革蜱血淋巴血浆孵育45分钟后，超过50%的螺旋体失去运动能力。两种不同蜱类反应的差异表明，肩突硬蜱在受到伯氏疏螺旋体攻击时具有免疫耐受性，依赖缓慢的吞噬反应从血淋巴中清除伯氏疏螺旋体。相比之下，变异革蜱具有高度免疫活性（即先天免疫），利用血浆杀伯氏疏螺旋体因子和吞噬细胞的快速增加来清除感染并限制组织入侵。
