Upon entry into the hemocoel of host insects, entomopathogenic fungi switch to yeast‐like hyphal bodies that are not recognized by host hemocytes and replicate extensively in the hemolymph. The mechanism by which hyphal bodies evade host cellular immunity is not well understood. This study compares Metarhizium rileyi conidia and hyphal bodies with respect to elicitation of the immune response of Helicoverpa armigera and recognition by host pattern recognition receptors (PRRs). We found that the ability of host hemocytes to phagocytize and nodulate hyphal bodies was weaker than those responses against conidia, suggesting that hyphal bodies are more able to evade host cellular immunity. Additionally, we found that the binding affinity of H. armigera β‐1,3‐glucan recognition proteins was much lower for hyphal bodies than for conidia. We observed no agglutination response of H. armigera C‐type lectin 3 (HaCTL3) against hyphal bodies, and HaCTL3 bound significantly less to hyphal bodies than to conidia, indicating that host PRRs have a lower affinity for hyphal bodies than for conidia. This study provides direct evidence that the mechanism whereby entomopathogenic fungi escape host cellular immunity involves the inability of host PRRs to sufficiently recognize hyphal bodies to elicit the cellular immune response.

中文翻译：

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棉铃虫逃脱细胞免疫反应的机制

进入宿主昆虫的血液囊中后，昆虫病原真菌会转变为酵母样的菌丝体，而宿主菌的血细胞无法识别这种菌丝，并在血淋巴中大量复制。菌丝体逃避宿主细胞免疫的机制尚不清楚。这项研究比较了金属假单胞菌分生孢子和菌丝体对棉铃虫免疫应答的诱导和宿主模式识别受体（PRR）的识别。我们发现宿主血细胞吞噬和结节菌丝体的能力比针对分生孢子的反应要弱，这表明菌丝体更能够逃避宿主细胞的免疫力。此外，我们发现棉铃虫的结合亲和力菌丝体的β-1,3-葡聚糖识别蛋白远低于分生孢子。我们没有观察到棉铃虫C型凝集素3（HaCTL3）对菌丝体的凝集反应，并且HaCTL3与菌丝体的结合明显少于对分生孢子的结合，这表明宿主PRR对菌丝体的亲和力比对分生孢子的亲和力低。这项研究提供了直接的证据，证明致病性真菌逃逸宿主细胞免疫的机制涉及宿主PRR无法充分识别菌丝体引发细胞免疫反应。