Development of two continuous hemocyte cell sublines in the Asian corn borer Ostrinia furnacalis and the identification of molecular markers for hemocytes

Effects of beauvericin on the blood cells of Bombyx mori

In this study, silkworms were treated by injection of the bioactive depsipeptide beauvericin (BEA) to explore its effect on the cellular immunity of larvae of the silkworm Bombyx mori. The results showed that: The LC50 of BEA for silkworms on the 3rd day of the 4th instar was 362.36 µM. The total count of circulating hemocytes in the silkworms decreased at 12 h after injection with 350 µM BEA, and reached the minimum value at 72 h post-treatment; at 48 h post-treatment, a large number of nodules formed by the aggregation of blood cells of the silkworms were observed under the light microscope. The survival rate of hemocytes in the larvae treated with BEA was significantly reduced in a dose-dependent manner in vivo and in vitro. The encapsulation of Q-Sepharose Fast Flow (QFF) gel particles by hemocytes in the treatment group was significantly higher than that in the control group at 1.5 h and 3 h post-treatment (P < 0.05). Moreover, the melanization ratio of QFF gel particles kept increasing with treatment time. The melanization rate at 24 h after treatment was significantly higher than that at other times (P < 0.05), reaching 55.33 %. Under the scanning electron microscope, BEA-treated larvae showed protrusions on the surface of their blood cells in vivo. Under the transmission electron microscope, it was observed that silkworm hemocytes were vacuolated. This study demonstrated that BEA had an effect on the blood cells of silkworms, and has thrown some light on the inhibitory effect and mechanism of BEA on insect cellular immunity.

Tachykinin-related peptides modulate immune-gene expression in the mealworm beetle Tenebrio molitor L

Tachykinins (TKs) are a group of conserved neuropeptides. In insects, tachykinin-related peptides (TRPs) are important modulators of several functions such as nociception and lipid metabolism. Recently, it has become clear that TRPs also play a role in regulating the insect immune system. Here, we report a transcriptomic analysis of changes in the expression levels of immune-related genes in the storage pest Tenebrio molitor after treatment with Tenmo-TRP-7. We tested two concentrations (10^-8 and 10^-6 M) at two time points, 6 and 24 h post-injection. We found significant changes in the transcript levels of a wide spectrum of immune-related genes. Some changes were observed 6 h after the injection of Tenmo-TRP-7, especially in relation to its putative anti-apoptotic action. Interestingly, 24 h after the injection of 10^-8 M Tenmo-TRP-7, most changes were related to the regulation of the cellular response. Applying 10^-6 M Tenmo-TRP-7 resulted in the downregulation of genes associated with humoral responses. Injecting Tenmo-TRP-7 did not affect beetle survival but led to a reduction in haemolymph lysozyme-like antibacterial activity, consistent with the transcriptomic data. The results confirmed the immunomodulatory role of TRP and shed new light on the functional homology between TRPs and TKs.

Cellular immune responses of the yellow peach moth, Conogethes punctiferalis (Lepidoptera: Crambidae), to the entomopathogenic fungus, Beauveria bassiana (Hypocreales: Cordycipitaceae)

The yellow peach moth (YPM), Conogethes punctiferalis, is a destructive insect pest of maize in eastern China and adapts to diverse environments, especially against pathogens. In insects, innate immunity comprising both humoral and cellular defense responses, is the primary defense against invading microbial pathogens. In this study, we identified five types of circulating hemocytes from the hemolymph of YPM larvae and analyzed their alterations and functions in immune responses to the infection of Beauveria bassiana, an entomopathogenic fungus infesting many lepidopteran species. The identified hemocytes included prohemocytes, plasmatocytes, granulocytes, spherulocytes and oenocytoids. Significant decreases of total and differential hemocyte counts were recorded over time in larvae, after they were injected with B. bassiana conidia. Additionally, hemocyte-mediated phagocytosis and nodulation were initiated in the hemolymph of larvae from the B. bassiana conidia challenge. The introduction of DEAE-Sepharose Fast Flow beads stained with Congo red also induced a strong encapsulation response in the larval hemolymph. Our observations unravel the occurrence of phagocytosis, nodulation and encapsulation in the hemocoel of YPM larvae to fight against the fungal infection, and offer the first insight into the YPM immune system.