Abstract
Although defensins have been isolated from a variety of metazoan, their role in cellular immunity has not been answered. In the study, we found that the hemocytes of the Manila clams Ruditapes philippinarum release defensin (designated as Rpdef3) in response to Vibrio parahaemolyticus challenge. The antimicrobial Rpdef3 was proved to be involved in the extracellular traps (ETs) that hemocytes released in response to Vibrio challenge. Scanning electron microscopy observation proved the patterns how ETs eliminate invading bacteria. Furthermore, Rpdef3 involved in ETs had broad-spectrum antimicrobial effect on both Gram-negative bacteria and Gram-positive bacteria. ELISA assay revealed that Rpdef3 could bind lipopolysaccharides and peptidoglycan in a dose-dependent manner. As concerned to the antibacterial mechanisms, Rpdef3 can cause bacterial membrane permeabilization, leading to cell death. As a result, Rpdef3 might contribute to the trap and the elimination of invading Vibrio in clam ETs. Taken together, our study suggest that the formation of ETs is a defense mechanism triggered by bacterial stimulation, coupled with antibacterial defensin.
Highlights
Antimicrobial peptides (AMPs) are essential part of the innate immune system in most organisms (Bulet et al, 2004)
Clam hemocytes were treated with V. parahaemolyticus, and the formation of extracellular traps (ETs) was determined by SytoX Green fluorescent staining
It was observed that V. parahaemolyticus obviously stimulated the formation of ETs-like structures in hemocytes of Manila clams
Summary
Antimicrobial peptides (AMPs) are essential part of the innate immune system in most organisms (Bulet et al, 2004). AMPs could be roughly divided into several groups based on their molecular structures and origins. Defensins are the first line of host innate immunity and eliminate invasive pathogens (Ayabe et al, 2004; Tincu and Taylor, 2004). They can be activated by interacting with the negatively charged membranes of bacteria, and leaded to the disruption of bacterial membrane and metabolic process (Boman et al, 1993; Park et al, 1998). Other immune functions of defensin have been demonstrated in invertebrates, such as inducing inflammation, suppressing inflammatory responses, and modulating immune
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