Mosquitoes are significant vectors of various pathogens. Unlike vertebrates, insects rely solely on innate immunity. Hemocytes play a crucial role in the cellular part of the innate immune system. The gaseous radical nitric oxide (NO) produced by hemocytes acts against pathogens and also functions as a versatile transmitter in both the immune and nervous systems, utilizing cyclic guanosine monophosphate (cGMP) as a second messenger. This study conducted a parallel comparison of NO synthase (NOS) expression and NO production in hemocytes during Escherichia coli K12 infection in four vector species: Aedes aegypti, Aedes albopictus, Culex pipiens molestus, and Culex pipiens quinquefasciatus. Increased NOS expression by NADPH diaphorase (NADPHd) staining and NO production by immunofluorescence against the by-product L-citrulline were observed in infected mosquito hemocytes distributed throughout the abdomens. NADPHd activity and citrulline labeling were particularly found in periostial hemocytes near the heart, but also on the ventral nerve chord (VNC). Pericardial cells of Ae. aegypti and Cx. p. molestus showed increased citrulline immunofluorescence, suggesting their involvement in the immune response. Oenocytes displayed strong NADPHd and citrulline labeling independent of infection status. This comparative study, consistent with findings in other species, suggests a widespread phenomenon of NO’s role in hemocyte responses during E. coli infection. Found differences within and between genera highlight the importance of species-specific investigations.

蚊子是多种病原体的重要传播媒介。与脊椎动物不同，昆虫仅依赖先天免疫。血细胞在先天免疫系统的细胞部分中发挥着至关重要的作用。血细胞产生的气态一氧化氮自由基 (NO) 可以对抗病原体，并且利用环磷酸鸟苷 (cGMP) 作为第二信使，在免疫和神经系统中充当多功能递质。本研究对四种媒介物种（埃及伊蚊、白纹伊蚊、猥亵库蚊和致倦库蚊）感染大肠杆菌K12期间血细胞中 NO 合酶 (NOS) 的表达和 NO 产生进行了平行比较。在分布于整个腹部的受感染蚊子血细胞中，通过 NADPH 黄酶 (NADPHd) 染色观察到 NOS 表达增加，并通过针对副产物 L-瓜氨酸的免疫荧光观察到 NO 产生增加。NADPHd 活性和瓜氨酸标记尤其在心脏附近的骨膜血细胞中发现，但也在腹神经索 (VNC) 上发现。Ae的心包细胞。埃及伊蚊和Cx。p。molestus显示出瓜氨酸免疫荧光增加，表明它们参与了免疫反应。卵细胞显示出强烈的 NADPHd 和瓜氨酸标记，与感染状态无关。这项比较研究与其他物种的研究结果一致，表明在大肠杆菌感染期间，NO 在血细胞反应中发挥着广泛的作用。属内和属间差异的发现凸显了物种特异性调查的重要性。