TABLE 1.

Immunomodulatory hookworm excretory/secretory proteins display documented or putative neutrophil‐specific functions

	Neutrophil‐related functions		Other immunomodulatory functions
L3 hookworm immuno‐evasion
DNase II N.br, N.am, A.ce	✓	Degrades DNA backbone of NETs 20	?	Could degrade ETs from other cells e.g. monocytes
ASP−2 A.ce, N.am	✓	Chemoattractant for neutrophils in vitro and in vivo 15	✓	Chemoattractant for monocytes induces antibody responses
KI−1 A.ce, A.ca	✓	Inhibits neutrophil elastase (low expression in L3) 51	✓	Inhibits trypsin and other elastases
HpARI* H.po			✓	Inhibits release of IL−33 alarmin 84
HpBARI* H.po			✓	Binds and blocks ST2 (IL−33 receptor) 85
MIF* A.ce	?	Binds the pro‐inflammatory MIF receptor (CD74) which increases MPO expression	?	Binds the pro‐inflammatory MIF receptor (CD74) on monocytes 86
MTP−2 A.ce			✓	Induces TNFα and IFNγ release from macrophages 87
PAF inhibitor N.br	✓	Inhibits PAF, a chemoattractant of eosinophils and neutrophils 35
Adult hookworm immuno‐evasion
TIL−1 A.ce, A.du	✓	Inhibits neutrophil elastase 52
APs A.ca			✓	Various anti‐coagulant peptides 88
NIF, Gp55 (H.co) A.ca, A.ce	✓	Blocks neutrophil migration via CD11b/CD18 integrin 37 , 40
Calreticulin(‐like) N.am	?	Prevents complement‐mediated neutrophil activation 89	✓	Prevents C1q deposition (from L4 to adult stage)
SODs N.am, A.ce, N.br	?	Protects against oxidation 90 , 91 , 92
PRXs A.ce	?	Protects against oxidation 93
TMP−1 A.ca			✓	De‐activates DCs, induces T regulatory cells, and inhibits matrix metalloproteases 94 , 95
TMP−2 A.ca			✓	Matrix metalloprotease inhibitor 94
Acetylcholinesterase N.am	?	Could prevent the release of neutrophil chemotactic factors from epithelial cells 96

✓, demonstrated function;?, putative or predicted function; *, also expressed in adults.

The third‐stage larvae (L3) and adult stages of hookworms and related STH express a number of excretory/secretory (ES) proteins, ⁷ some with known or putative anti‐neutrophil activity.

Of the 8 characterized proteins secreted by hookworm infective larvae or their laboratory model counterparts, 5 have confirmed or putative activity associated with neutrophils. Two are related to chemotaxis (ASP‐2 as attractant ¹⁵ and PAF inhibitor as blocker ³⁵ ). The three others could impair NETs formation (DNase‐II ²⁰ , KI‐1 ⁵¹ and MIF ⁷ , ⁸⁶ ). Two ES not associated with neutrophils have been discovered in Heligmosmoides polygyrus and inhibit IL‐33/ST2 pathway (HpARI and HpBARI ⁸⁴ , ⁸⁵ ). Finally, MTP‐2 is an astacin‐like metalloprotease that enhances the expression of TNFα and IFNγ in classically activated (LPS‐stimulated) macrophages. ⁸⁷

In the adult stage, more proteins with immunomodulatory properties have been characterized. Of 12 notable proteins we could find described in the literature, 7 had potential anti‐neutrophil activity. NIF, ³⁷ and its homologue gp55 ⁴⁰ in H. contortus, block neutrophil chemotaxis. Acetylcholinesterase could also decrease neutrophil recruitment indirectly by blocking epithelial cells chemokine secretions. ⁹⁶ Once again, several ES protein activities were consistent with anti‐NET activity (TIL‐1, MIF, SODs, PRXs). Similar to KI‐1, TIL‐1 has been shown to inhibit NE. ⁵² Both SODs ⁹⁰ , ⁹¹ , ⁹² and PRXs ⁹³ could affect NETosis by decreasing oxidative stress. Finally, a calreticulin‐like protein, identified in Necator americanus could contribute to complement evasion, ⁸⁹ and thus indirectly decrease neutrophil trapping and NETosis. Non‐neutrophil‐related proteins include metalloprotease inhibitors (TMP‐1 and 2), which have been shown to affect dendritic cell polarization and inhibit host matrix metalloproteases (MMP)‐2, −7, and −13. ⁹⁴ , ⁹⁵ APs have been shown to have anticoagulant activity. ⁸⁸

Checkmark indicates function described in vivo or in vitro, interrogation mark indicates putative function from known activity of protein or predicted function of sequence.

Abbreviations: A.ca, A. caninum; A.ce, A. ceylanicum; Ac‐TMP‐2, tissue inhibitor of metalloprotease 2; A.du, A. duodenale; APs, anticoagulant proteins; ASP‐2, ancylostoma‐secreted proteins; H.co, H. contortus; KI‐1, Kunitz‐type inhibitor 1 from Ancylostoma ceylanicum; MIF homologue of macrophage migration inhibitory factor; MTP‐2, metalloprotease 2; N.am, N. americanus; N.br, N. brasiliensis; TIL‐1 trypsin‐inhibtor like serine protease inhibitor.

The color is to help the reader assess if the evasion products has been linked to neutrophil quickly. Dark blue is used for when Neutro association is demonstrated, light blue, when it is hypothetical and grey for a mechanism unrelated to neutrophil.