The broader secretome of Necator americanus, the human hookworm, encompasses the full array of excretory-secretory (ES) products released by larval and adult stages to facilitate infection, survival, and host modulation. This includes not only the enzymes discussed previously (e.g., proteases for tissue penetration and nutrient digestion) but also a diverse set of non-enzymatic proteins, antioxidants, inhibitors, and other molecules. Genomic and proteomic analyses reveal a secretome of approximately 198 proteins in adult ES products, with expansions in key families tailored for parasitism in humans. Around 33% of the parasite’s proteome is predicted to be secreted, including 1,590 classical (signal peptide-bearing) and 4,785 non-classical secreted proteins. These components enable the parasite to evade immune detection, suppress excessive inflammation, promote wound healing, and establish chronic infections, often shifting the host response from pro-inflammatory Th1/Th17 to anti-inflammatory Th2/regulatory profiles.
Major Components of the Secretome
The secretome is dominated by several protein families, with proteases comprising about 13-15% (as previously detailed), but the majority are non-enzymatic. Key categories include:
– Most abundant group (27-35% of ES proteins, ~54-137 total in the genome, including single- and double-domain variants).
– Examples: Na-ASP-2 (from infective larvae).
– Functions: Cysteine-rich proteins involved in infection establishment, stage transitions, and host-parasite interactions. Many are immunogenic, recognized by IgG in infected humans, making them diagnostic or vaccine candidates (e.g., Na-ASP-2 induces neutrophil recruitment and is a phase I vaccine target). They bind host proteins, potentially disrupting immune signaling.
– Examples: Glutathione S-transferases (GSTs, e.g., Na-GST-1), peroxiredoxins (PRX), copper/zinc superoxide dismutases (Cu/Zn SOD).
– Functions: Protect the parasite from host-generated reactive oxygen species (ROS) during oxidative bursts. They neutralize free radicals, supporting survival in inflammatory environments.
– Examples: Serine protease inhibitors (SPIs, 87 in genome, mostly Kunitz-type), tissue inhibitors of metalloproteases (TIMPs).
– Functions: Inhibit host digestive enzymes and coagulation factors, preventing blood clotting during feeding and protecting against intestinal proteases. They also contribute to anticoagulation and immune evasion.
– Examples: Galectins, C-type lectins, calreticulin.
– Functions: Bind carbohydrates or host cells, modulating complement activation and cell adhesion (e.g., inhibiting neutrophil adhesion).
– Examples: Macrophage migration inhibitory factors (MIF), neutrophil inhibitory factor (NIF), hookworm platelet inhibitor (HPI), TGF-β homologs.
– Functions: Mimic or interfere with host cytokines, promoting anti-inflammatory effects and wound healing.
– Abundant (~21-42 proteins with domains of unknown function).
– Functions: Largely uncharacterized, but likely contribute to unique host interactions; many lack GO annotations.
Other components include globins (for oxygen transport) and exosomes/vesicles that package these molecules for delivery to host cells.
Overall Functions
The secretome supports parasitism by enabling tissue migration, blood feeding, and nutrient acquisition while evading host defenses. Adult-stage proteins are enriched for blood processing and anticoagulation, while larval ones focus on invasion. Many proteins are human-specific, with phylogenetic clustering distinct from animal hookworms, reflecting adaptation to human hosts.
Effects on Inflammation Signaling
The secretome’s immunomodulatory arsenal dampens host inflammation to prevent expulsion and tissue damage:
Therapeutic Implications
The secretome’s anti-inflammatory properties inspire “helminth therapy” for autoimmune diseases (e.g., IBD, MS, allergies), with controlled infections or recombinant proteins in trials. Proteins like Na-ASP-2 and Na-GST-1 are vaccine candidates against hookworm, while others (e.g., MIF, NIF) are explored for stroke or inflammation treatments. Ongoing research compares it to other hookworms (e.g., A. ceylanicum) for conserved vs. species-specific targets.
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Necator americanus Secretome Citation Summary
Genomic and proteomic studies identify approximately 198 proteins in the adult excretory-secretory (ES) products of Necator americanus, with about 33% of the parasite’s proteome predicted to be secreted, including 1,590 classical and 4,785 non-classical secreted proteins [1][2][3]. These ES products encompass enzymes like proteases (13-15%), alongside dominant non-enzymatic families such as SCP/TAPS proteins (27-35%, ~54-137 total), antioxidants, inhibitors, lectins, cytokine modulators, and hypothetical proteins [1][2][4]. The secretome facilitates infection, immune evasion, inflammation suppression, and chronic survival by shifting host responses from Th1/Th17 to Th2/regulatory profiles [1][5][6].
Key Protein Families
SCP/TAPS proteins, exemplified by Na-ASP-2 from infective larvae, dominate the ES secretome and function in infection establishment, host interactions, and immunogenicity, serving as vaccine candidates that induce neutrophil recruitment [1][7][4]. Antioxidants like glutathione S-transferases (Na-GST-1), peroxiredoxins, and Cu/Zn superoxide dismutases neutralize host reactive oxygen species (ROS) for parasite protection in inflammatory sites [1][8][9]. Protease inhibitors include serine protease inhibitors (87 Kunitz-type in genome) and tissue inhibitors of metalloproteases (TIMPs), which block host enzymes, prevent clotting, and aid immune evasion [2][10][11][12].
Lectins (galectins, C-type), calreticulin, and binding proteins modulate complement, cell adhesion, and neutrophil function [13][14]. Cytokine homologs such as macrophage migration inhibitory factor (MIF), neutrophil inhibitory factor (NIF), hookworm platelet inhibitor (HPI), and TGF-β mimics promote anti-inflammatory effects, wound healing, and Treg induction [15][16][6]. Hypothetical proteins with domains of unknown function (~21-42) likely support unique host interactions [1].
Immunomodulatory Effects
ES products dampen pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-12), cleave chemokines to limit eosinophils, inhibit NF-κB/inflammasome, and counter ROS, while favoring Th2 cytokines (IL-4, IL-10, IL-13) and hyporesponsiveness [8][5][6]. They interact with NK cells (selective IFN-γ), neutrophils, eosinophils, and PBMCs to suppress Th1/Th17 and enhance regulatory responses [5][6]. Adult proteins emphasize blood processing/anticoagulation, larval ones invasion [2].
Therapeutic Potential
Na-ASP-2 and Na-GST-1 are phase I vaccine candidates reducing worm burdens via antibody-mediated hemoglobin digestion interference [1][4][9][17]. Secretome components inspire helminth therapy for IBD, MS, and allergies through anti-inflammatory effects, with parallels to other hookworms like A. ceylanicum [11][9].
Citation List
Citations:
[1] Comprehensive analysis of the secreted proteome of adult Necator … https://pmc.ncbi.nlm.nih.gov/articles/PMC7274458/
[2] Genome of the human hookworm Necator americanus – Nature https://www.nature.com/articles/ng.2875
[3] Genome of the human hookworm Necator americanus – PMC – NIH https://pmc.ncbi.nlm.nih.gov/articles/PMC3978129/
[4] Comprehensive analysis of the secreted proteome of adult Necator … https://journals.plos.org/plosntds/article?id=10.1371%2Fjournal.pntd.0008237
[5] Stage-specific immune responses in human Necator americanus … https://pmc.ncbi.nlm.nih.gov/articles/PMC1976388/
[6] Immunobiology of hookworm infection – Oxford Academic https://academic.oup.com/femspd/article/43/2/115/604248
[7] Necator americanus Ancylostoma secreted protein-2 (Na-ASP-2 … https://www.biorxiv.org/content/10.1101/2020.08.07.224964.full
[8] Necator Americanus – an overview https://www.sciencedirect.com/topics/immunology-and-microbiology/necator-americanus
[9] Safety and immunogenicity of the Na-GST-1 hookworm vaccine in … https://pmc.ncbi.nlm.nih.gov/articles/PMC5441635/
[10] Protease Inhibitors from Marine Venomous Animals and Their … https://pmc.ncbi.nlm.nih.gov/articles/PMC3721222/
[11] The Hookworm Tissue Inhibitor of Metalloproteases (Ac-TMP-1 … https://journals.plos.org/plosntds/article?id=10.1371%2Fjournal.pntd.0000439
[12] TIMPs of parasitic helminths – a large-scale analysis of high … https://pmc.ncbi.nlm.nih.gov/articles/PMC3679795/
[13] The many faces of parasite calreticulin – PMC – PubMed Central https://pmc.ncbi.nlm.nih.gov/articles/PMC10040973/
[14] A calreticulin-like molecule from the human hookworm Necator … https://pubmed.ncbi.nlm.nih.gov/11240905/
[15] Nematode Orthologs of Macrophage Migration Inhibitory Factor (MIF) as … https://pmc.ncbi.nlm.nih.gov/articles/PMC8877345/
[16] The structure of hookworm platelet inhibitor (HPI), a CAP … – NIH https://pmc.ncbi.nlm.nih.gov/articles/PMC4461323/
[17] Altering the intracellular trafficking of Necator americanus GST-1 … https://pmc.ncbi.nlm.nih.gov/articles/PMC11756802/
[18] [PDF] Characterisation of Necator americanus excretory/secretory products https://researchonline.jcu.edu.au/67910/1/JCU67910Logan2019thesis.pdf
[19] Rodent Models for the Study of Soil-Transmitted Helminths – Frontiers https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.639573/full