Necator americanus: The Na-ASP-2 protein secreted by the infective larvae induces neutrophil recruitment in vivo and in vitro

Abstract

The L3-secreted Ancylostoma Secreted Protein-2 from the human hookworm Necator americanus (Na-ASP-2) has been selected as a candidate vaccine antigen in anticipation of clinical trials. Its crystal structure revealed that Na-ASP-2 has structural and charge similarities to CC-chemokines, suggesting that it might act as a chemokine mimic when released by the infective larvae during tissue migration. Using the air pouch model of acute inflammation, we found that Na-ASP-2 induced a significant leukocyte influx to the skin pouch, mostly comprised of neutrophils (60%) and monocytes (30%) that was transient and resolved in 24 h. Other hookworm larval proteins did not cause any inflammatory leukocytes to migrate into air pouches. In vitro chemotaxis assays confirmed our results and demonstrated that leukocyte migration was a direct effect of Na-ASP-2 exposure and not caused by other molecules released by host cells in the inflammatory microenvironment or by the expression vector.

Secreted Proteomes of Different Developmental Stages of the Gastrointestinal Nematode Nippostrongylus brasiliensis

“…In contrast, the most abundant protein in adult worms was an ASP that shared sequence identity with N. americanus ASP-2. Na-ASP-2 is only expressed by hookworm L3 and not by the adult stages, and has been extensively explored as a vaccine candidate (67,68).…”

Neutrophil and eosinophil chemotactic factors in the excretory/secretory products of sheep abomasal nematode parasites

“…At high concentrations of a chemotactic factor, the number of migrating cells usually levels off or even declines. Numerous other helminths also contain and release an NCF, including the nematodes N. americanus (Bower et al 2008), O. aculeatum and O. volvulus (Rubio de Krömer et al 1998), A. suum and T. canis (Falcone et al 2001), D. immitis (Horii et al 1986b) and Trichinella spp. (Shupe and Steward 1991).…”

“…These include L3, L4 and adult Teladorsagia circumcincta and Haemonchus contortus (Wildblood et al 2005), L3 Ostertagia ostertagi (Klesius et al 1985(Klesius et al , 1986, L3 Anisakis (Tanaka and Torisu 1978), adult Ascaris (Tanaka et al 1979), adult Angiostrongylus cantonensis (Ishida and Yoshimura 1990), adult Dirofilaria immitis (Owhashi et al 1996), Metastrongylus apri (Sasaki and Katsuno 1983), larval Trichinella spiralis and adult Trichuris muris (Dixon et al 2006). Neutrophil chemotactic factors (NCF) have been identified in parasitic cestodes (Horii et al 1984a) and trematodes (Horii et al 1984b;Jefferies et al 1996;Owhashi et al 2005), as well as Tritrichomonas foetus (Owhashi et al 1994), Necator americanus (Bower et al 2008), Oesophagostomum aculeatum , adult Ascaris (Tanaka et al 1979), D. immitis (Horii et al 1986b) and Oesophagostomum volvulus (Rubio de Krömer et al 1998), Trichinella spp. (Shupe and Steward 1991), Ascaris suum and Toxocara canis (but not Anisakis simplex; Falcone et al 2001).…”

Probing the equatorial groove of the hookworm protein and vaccine candidate antigen, Na-ASP-2

“…SK small conductance calcium-activated potassium channels are comprised of heteromeric channels formed by SK1 (K Ca 2.1), SK2 (K Ca 2.2) and SK3 (K Ca 2.3) (Monaghan et al, 2004). Intriguingly, Na-ASP-2 is able to induce neutrophil recruitment into areas of acute inflammation, and it has been speculated that this may act as a promoting factor of inflammation during tissue migration to increase tissue permeability (Bower et al, 2008). SK channels mediate the production of reactive oxygen species that may be used for oxidative destruction of pathogens (Fay et al, 2006).…”

“…Na-ASP-2 from the human hookworm Necator americanus is a member of the Group 1 ASPs, and its crystal structure has previously been determined (Asojo et al, 2005). Based on the observation that Na-ASP-2 induces neutrophil and monocyte migration (Bower et al, 2008), it has been proposed that this molecule may be an antagonistic ligand of complement receptor 3 (CR3) and affects the immune cascade by preventing the binding of chemotaxin (Asojo et al, 2005). …”