AUTHOR=Dong Zhaoming , An Lingna , Lu Mengyao , Tang Muya , Chen Haiqin , Huang Xuan , Hou Yong , Shen Guanwang , Zhang Xiaolu , Zhang Yan , Xia Qingyou , Zhao Ping 

TITLE=SPINK7 Recognizes Fungi and Initiates Hemocyte-Mediated Immune Defense Against Fungal Infections

JOURNAL=Frontiers in Immunology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2021.735497

DOI=10.3389/fimmu.2021.735497

ISSN=1664-3224

ABSTRACT=<p>Serine protease inhibitors of Kazal-type (SPINKs) were widely identified in vertebrates and invertebrates, and played regulatory roles in digestion, coagulation, and fibrinolysis. In this study, we reported the important role of SPINK7 in regulating immune defense of silkworm, <italic>Bombyx mori</italic>. SPINK7 contains three Kazal domains and has 6 conserved cysteine residues in each domain. Quantitative real-time PCR analyses revealed that <italic>SPINK7</italic> was exclusively expressed in hemocytes and was upregulated after infection with two fungi, <italic>Saccharomyces cerevisiae</italic> and <italic>Candida albicans</italic>. Enzyme activity inhibition test showed that SPINK7 significantly inhibited the activity of proteinase K from <italic>C. albicans</italic>. Additionally, SPINK7 inhibited the growth of three fungal spores, including <italic>S. cerevisiae</italic>, <italic>C. albicans</italic>, and <italic>Beauveria bassiana</italic>. The pathogen-associated molecular patterns (PAMP) binding assays suggested that SPINK7 could bind to β-D-glucan and agglutinate <italic>B. bassiana</italic> and <italic>C. albicans</italic>. <italic>In vitro</italic> assays were performed using SPINK7-coated agarose beads, and indicated that SPINK7 promoted encapsulation and melanization of agarose beads by <italic>B. mori</italic> hemocytes. Furthermore, co-localization studies using immunofluorescence revealed that SPINK7 induced hemocytes to aggregate and entrap the fungi spores of <italic>B. bassiana</italic> and <italic>C. albicans</italic>. Our study revealed that SPINK7 could recognize fungal PAMP and induce the aggregation, melanization, and encapsulation of hemocytes, and provided valuable clues for understanding the innate immunity and cellular immunity in insects.<bold /></p>