Expression profiling and binding properties of fibrinogen-related proteins (FREPs), plasma proteins from the schistosome snail host Biomphalaria glabrata

Abstract

A growing body of evidence suggests an important role for fibrinogen-like proteins in innate immunity in both vertebrates and invertebrates. It has been shown that fibrinogen-related proteins (FREPs), plasma proteins present in the freshwater snail Biomphalaria glabrata, the intermediate host for the human blood fluke Schistosoma mansoni, are diverse and involved in snail innate defense responses. To gain further insight into the functions of FREPs, recombinant FREP proteins (rFREPs) were produced in Escherichia coli and antibodies (Abs) were raised against the corresponding rFREPs. We first show that most FREP proteins exist in their native conformation in snail hemolymph as multimeric proteins. Western blot analyses reveal that expression of multiple FREPs including FREP4 in plasma from M line and BS-90 snails, which are susceptible and resistant to S. mansoni infection, respectively, is up-regulated significantly after infection with the trematode Echinostoma paraensei. Moreover, our assays demonstrate that FREPs are able to bind E. paraensei sporocysts and their secretory/excretory products (SEPs), and a variety of microbes (Gram-positive and Gram-negative bacteria and yeast). Furthermore, this binding capability shows evidence of specificity with respect to pathogen type; for example, 65-75-kDa FREPs (mainly FREP4) bind to E. paraensei sporocysts and their SEPs whereas 95-kDa and 125-kDa FREPs bind the microbes assayed. Our results suggest that FREPs can recognize a wide range of pathogens, from prokaryotes to eukaryotes, and different categories of FREPs seem to exhibit functional specialization with respect to the pathogen encountered.

Single Sea Urchin Phagocytes Express Messages of a Single Sequence from the DiverseSp185/333Gene Family in Response to Bacterial Challenge

“…Expanded immune response diversity in arthropods may be derived from the single copy DSCAM gene through regulated alternative splicing in hemocytes that produce many DSCAM isotypes (46,47) that have important pathogen opsonization functions leading to augmented phagocytosis by hemocytes (48). Somatic DNA modifications that broaden the sequence diversity of the FREP gene family in freshwater snails generate diversity in the encoded proteins (6), which are involved in snail protection against digenean parasites and other pathogens (49,50). Diversification of the FREP genes is thought to occur in individual hemocytes (51), although the expression patterns in single hemocytes are not known.…”

Role for a somatically diversified lectin in resistance of an invertebrate to parasite infection

“…Immune-related molecules containing fibrinogen domains have been identified in a steadily increasing number of invertebrate phyla (15,(35)(36)(37)(38)(39), however gastropod FREPs are structurally unique and, thus far, have not been found outside the Phylum Mollusca. FREPs change in abundance in snail hemolymph following digenean infection (15,35,36) and can precipitate secretory/excretory products of sporocysts implying they play a role in response to infections (15). FREPs have recently been shown to form complexes with highly polymorphic mucin molecules produced by S. mansoni sporocysts, complexes that also include thioester-containing proteins believed to favor phagocytosis and encapsulation responses (40).…”

Characteristic and functional analysis of a ficolin-like protein from the oyster Crassostrea hongkongensis

“…These proteins are up-regulated following exogenous immuno-stimulation and could bind to pathogens to eliminate foreign invaders. Thus, FREPs are important members of the host innate immune response against pathogens [9,17,18]. Many FREPs have been identified in different animal species, including vertebrates, urochordates and invertebrates [7,14,16].…”